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Antenatal fetal surveillance “Assessment of the AFV”
Accepted Manuscript Antenatal Fetal Surveillance “Assessment of the AFV” Dawn S. Hughes, MD, Everett F. Magann, MD
PII:
S1521-6934(16)30077-3
DOI:
10.1016/j.bpobgyn.2016.08.004
Reference:
YBEOG 1636
To appear in:
Best Practice & Research Clinical Obstetrics & Gynaecology
Received Date: 1 April 2016 Revised Date:
10 June 2016
Accepted Date: 8 August 2016
Please cite this article as: Hughes DS, Magann EF, Antenatal Fetal Surveillance “Assessment of the AFV”, Best Practice & Research Clinical Obstetrics & Gynaecology (2016), doi: 10.1016/ j.bpobgyn.2016.08.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Antenatal Fetal Surveillance “Assessment of the AFV”
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Dawn S. Hughes, MD; Everett F. Magann, MD Department of Obstetrics and Gynecology, University of Arkansas for Medical Sciences, Little Rock, AR, USA Corresponding author: Everett F. Magann, MD
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Department of Obstetrics & Gynecology, UAMS 4301 W. Markham St. Slot # 518, Little Rock, AR 72205, USA
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Phone: 001-501-686-8345; Fax: 001-501-526-7820; Email: [email protected]
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ABSTRACT The evaluation of AFV is an established part of the antenatal surveillance of pregnancies at risk
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for an adverse pregnancy outcome. The two most commonly used ultrasound techniques to
estimate AFV are the amniotic fluid index (AFI) and the single deepest pocket (SDP). Four
studies have defined normal AFVs and, although their normal volumes have similarities, there
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are also differences primarily due to the statistical methodology used in each study. Dye-
determined AFV correlates with ultrasound estimates for normal fluid volumes but correlates
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poorly for oligohydramnios and polyhydramnios. The addition of colour Doppler in estimating AFV leads to the over diagnosis of oligohydramnios. Neither the AFI nor the SDP is superior in identifying oligohydramnios, but the SDP is a better measurement choice as the use of AFI increases the diagnosis rate of oligohydramnios and labour inductions without an improvement
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in pregnancy outcomes.
KEYWORDS: AFV; Oligohydramnios; Polyhydramnios; Pregnancy
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Introduction
The assessment of amniotic fluid volume (AFV) is an established part of the antenatal fetal
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surveillance of a pregnancy at risk for an adverse pregnancy outcome. The gold standard for antenatal surveillance for many US-based investigators is the contraction stress test (CST), which has a false negative rate of .4/1000. However, because of the necessity to have either spontaneous contractions or to start an intravenous line and induce contractions with oxytocin and the high false positive results, this test is less frequently used today [1]. Currently, two commonly used antenatal tests are the BPP (biophysical profile) and the modified BPP. The
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components of the BPP include non-stress test or cardiotocography, fetal breathing, fetal movement, fetal tone and AFV assessment. [2] The components of the modified BPP include non-stress test or cardiotocography and AFV assessment. [3] Both tests estimate the AFV by
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ultrasound as an essential component of the antenatal test. Both tests have good reliability with a false negative rate of .6/1000 for the BPP and a false negative rate of .8/1000 for the modified BPP [4]. The significance of estimating the AFV is underscored with the modified BPP. The
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false negative rate is observed to increase to 1.9-5/1000 when the non-stress
test/cardiotocography is done as a stand-alone test without an estimation of the AFV [5]. (Table
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1) The CST is able to identify both acute and chronic stress by the presence of repetitive late decelerations, whereas the BPP can only identify acute stress. The modified BPP is able to identify both acute and chronic stress by the addition of the AFV measurement. It is believed that the fetus under chronic stress will shunt blood to the brain, heart, and adrenal glands at the
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expense of other bodily organs. This shunting of blood away from the kidneys results in decreased renal perfusion and, consequently, to decreased fetal urinary output. This ultimately causes a decrease in the AFV. Therefore, the estimation of AFV by ultrasound is believed to aid
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in the recognition of the fetus under chronic stress that results from utero-placental insufficiency.
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The Pathophysiology of Amniotic Fluid
Amniotic fluid provides a supportive and protective environment for fetal development during gestation by protecting the fetus from trauma, possessing bacteriostatic properties, allowing for fetal movement and thus fostering development of the limbs and lungs and preventing compression of the umbilical cord [6]. The dynamics of the regulation of AFV are complex, with the entire volume of AF turning over on a daily basis [7]. The production and resorption of AFV is influenced by several sources, including fetal urination, fetal swallowing, fluid production by
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the fetal lung, skin and oral-nasal cavities, the intramembranous pathway, and the transmembranous pathway [8]. Fetal urine production is the main contributor to AFV in the
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second half of pregnancy [9]. What is Normal Amniotic Fluid Volume?
It is important to clearly define what a normal AFV is in order to then identify what is abnormal.
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The definition is an important one because it impacts pregnancy management. Multiple studies have shown that low abnormalities of AFV (oligohydramnios) have been associated with adverse
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pregnancy outcomes [10, 11, 12]. Multiple definitions of what constitutes an abnormal AFV can be found in the literature [9]. Oligohydramnios, or low AFV, has been defined as less than 200 mL [13], less than 500 mL total volume [14,15], less than the 5th percentile for gestational age [16], as SDP less than 2cm [17, 18, 19], an AFI of less than 5 cm [10, 11, 19, 20, 21], or an AFV
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that is subjectively low [22]. Polyhydramnios, or an increased AFV, has been defined as a total volume that is greater than 2000 mL [23], an AFV that is greater than the 95th percentile for gestational age [20], an SDP of greater than 8 cm [24], an AFI of greater than 24 cm [25] or
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greater than 25 cm [26], or an AFV that is subjectively increased [22]. There are 4 studies which have defined normal AFV across gestation. Brace et al. derived
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from the literature normal volumes using dye-dilution techniques and direct measurements at the time of hysterotomy of 705 pregnancies without fetal anomalies, maternal or fetal disease, fetal death, or spontaneous abortion [27]. The investigators observed that the AFV did not change significantly between 22 and 39 weeks. The AFV peaked between 33 to 34 weeks with a subsequent decline thereafter. Magann et al evaluated 144 normal pregnancies in a singleton institution using dye-dilution techniques to create a growth curve of normal pregnancies across
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gestation. The investigators observed that the AFV continued to increase during gestation, peaking at 40 weeks [28]. Queenan et al. also used dye-dilution techniques to assess 172 patients between 15 to 42 weeks and observed a peak of AFV at 33 to 34 weeks with a decline thereafter
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[29]. Sandlin et al evaluated 379 normal pregnancies from 16-41 weeks (144 of these
pregnancies had been previously reported by Magann [28]) using both dye-dilution techniques and direct measurement at the time of Caesarean section and used modelling by quantile
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regression to create a normative chart of AFV across gestation with a peak at 38 weeks [30]. There are similarities but also differences in their normal volumes across gestation primarily due
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to the statistical methods used. (Figure 1) As evidenced by these studies, there is not yet a clearly defined value for a “normal” AFV. What should define normal is a value that is neither excessively high nor low; what should drive the definition of abnormal is poor clinical outcomes associated with such measurements.
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Correlation of Dye-Determined or Directly Measured AFV to Ultrasound Estimates of Amniotic Fluid Volume
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There have been a number of investigations that have correlated the ultrasound estimate of AFV to a true volume of amniotic fluid (dye determined or directly measured at the time of Caesarean
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section). In a study of 5 near term sheep presented as an abstract at the Society of Gynecological Investigation in 1988, the amniotic and allantoic fluid was drained from the sheep and the uteri were filled with 2 to 2.5 liters of normal saline. At each 100 ml infusion of saline, an AFI was done. Using curve fitting formulas, there was good correlation between the increasing AFI and the amount of saline infused (r=0.94). Unfortunately, in a study by Sepulveda in 16 pregnancies with mid-gestation oligohydramnios, the correlation of the infused saline with an increasing AFI was not as good [31]. These women underwent amniocentesis with infusions of saline and
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ultrasound estimates of AFV using the SDP and AFI. It was observed that only 30% of the variation of the ultrasounds could be explained by the saline infusion. Croom et al correlated AFI and SDP with dye-determined volumes of 50 women undergoing Caesarean deliveries and found
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good correlation but only 2 pregnancies had oligohydramnios and none had polyhydramnios [32]. Dildy et al, correlating the ultrasound measurements with dye-determined fluid AFV,
observed that the AFI overestimated AFV by 89% at low volumes and by 54% at high volumes
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[15]. Magann et al in 2 studies showed that the correlation of the AFI with normal fluid was good, but when the AFV was low, the sensitivity of the AFI to detect oligohydramnios was only
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6.7% in one study and 8.7% in the second study [33, 34]. Horsager et al observed, in a study that correlated ultrasound estimate with directly measured AFV at the time of Caesarean delivery, that the sensitivity of the AFI to detect directly measured oligohydramnios was only 18% [35]. Magann, in a study of the SDP to detect oligohydramnios, observed that only 14% of the dye-
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determined oligohydramnios pregnancies were identified by using the SDP technique [36]. In the largest study correlating the SDP and AFI with dye determined AFV, both the AFI (sensitivity 10% and specificity 96%) and the SDP (sensitivity 5% and specificity 98%) were unreliable in
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identifying oligohydramnios [37]. These studies consistently document that the ultrasound estimate of AFV correlates well with normal dye-determined or directly measured AFVs but
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poorly with true volumes of abnormal fluid volumes (oligohydramnios and polyhydramnios). Magann et al has also shown that the accuracy of determining normal AFV was not improved by combining commonly used US techniques including AFI, SDP, 2-diameter pocket technique and subjective assessment [38]. It was also noted that simple subjective assessment of AFV by a trained sonographer appears to be just as accurate as the more complex ultrasonic measurements of determining abnormal AFVs.[22] (Table 2)
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Two investigations have compared the normative datasets of Brace et al [27] and Magann et al [28] in the detection of low, normal, and polyhydramnios using fixed cut offs stratified by gestational age and in the correlation of AFI and the SDP to the modelled growth curves. In the
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first study, the fixed cut offs of AFV of < 500 ml was classified as oligohydramnios, 500-2000 ml as normal AFV and > 2000 ml as polyhydramnios [39]. The study found that Brace and Magann databases classified the AFVs differently 24% of the time. The Brace dataset classified
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19% of the volumes as oligohydramnios, 71% as normal AFV, and 10% as polyhydramnios. On the other hand, the Magann dataset classified 3% as oligohydramnios, 83% as normal AFV and
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14% as having polyhydramnios. The authors concluded that the two datasets were not exchangeable and that abnormal volumes cannot be clearly identified until normal volumes are defined. An investigation that assessed the correlation between the AFI and SDP techniques with the AFV as modelled by normal curves of Brace and Magann revealed that, overall, there
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was good correlation between the AFI and SDP and the actual volumes of both Brace [27] and Magann [28] [36]. The AFI normal ranges of 5.1 - 20 versus 5.1 - 24 was better correlated with the normal volumes of both Brace and Magann. The AFI and SDP better predict
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oligohydramnios using the Brace model, while the Magann model more accurately predicts normal AFV and polyhydramnios. The authors suggested that future investigations would need
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to focus on emerging statistical methodologies to create normal curves which will be better able to define abnormal AFVs.
Estimate of AFV using Ultrasound
While measurement of AFV using dye-dilution techniques or direct measurement at time of Caesarean delivery are the most accurate methods to determine the actual AFV, these methods are invasive, labour-intensive, and the measurement technique can only be done at the time of
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Caesarean delivery. Therefore, AFV is frequently estimated using ultrasonography [40]. The two techniques most frequently used to measure AFV are the AFI and the SDP. The AFI is calculated by the operator first dividing the uterine cavity into four quadrants, and then measuring the fluid
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pocket with the largest vertical diameter within each quadrant. Each pocket must have a
horizontal diameter of at least 1 cm, and the operator must keep the transducer perpendicular to the floor and not the uterine contour. Measurement of a pocket in which there is the brief
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appearance of the umbilical cord is acceptable, but if it remains in the pocket, then another
pocket should be measured. The sum of these four measurements is then calculated to determine
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the AFI [41]. An AFI of <5 is defined as oligohydramnios, 5-24 or 25 as normal and > 24 or 25 as polyhydramnios. The SDP is calculated by measuring the vertical dimension of the largest pocket of amniotic fluid that does not contain umbilical cord or fetal extremities with a horizontal measurement of at least 1 cm. It is also important that the SDP is measured at a right
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angle to the floor and not the uterine contour. An SDP of < 2 is classified as oligohydramnios, 28 as normal, and >8 as polyhydramnios [2].
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Should the Ultrasound Estimate of AFV Be Done with Colour Doppler or Gray Scale? The initial assessments to estimate the AFV, the SDP of the BPP, and the AFI of the modified
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BPP were done using gray scale assessment. If there were multiple loops of cord, or if there were small parts in the pocket, then that pocket of fluid was not measured. Colour Doppler has recently been used to assist in the identification of amniotic fluid pockets containing umbilical cord that may not be seen with gray scale imaging alone. It was felt important to identify pockets with umbilical cord in them that may not have been seen with gray scale imaging alone because those pockets would have been excluded from measurement based on the original methods using gray scale alone. The better detection of pockets containing umbilical cord using colour Doppler,
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it was thought, would be a better identifier of oligohydramnios (Figure 2). In a study by Bianco et al., the use of colour Doppler compared to gray scale significantly decreased the AFI and increased the number of pregnancies classified as having oligohydramnios [42]. In another study
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by Goldkrand et al., the investigators also observed that the AFI was less with Colour Doppler compared to gray scale [43]. Magann et al. observed that the AFI was reduced by approximately 20% when colour Doppler was compared to gray scale [44]. The investigators evaluated 67
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women to determine if the use of colour Doppler increased the detection of dye-determined oligohydramnios, normal AFV, and polyhydramnios. The use of colour Doppler compared to
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gray scale increased the proportion of women classified as having oligohydramnios. However, the use of colour Doppler did not accurately identify any more women with actual dyedetermined oligohydramnios, but instead labelled 9 additional women with normal dyedetermined AFV as having oligohydramnios. The authors concluded that the use of colour
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Doppler leads to the over diagnosis of oligohydramnios [44].
Most of the original investigations that set the thresholds of an AFI of <5 or an SDP of < 2 to categorize a pregnancy as having oligohydramnios, and potentially at-risk for an adverse
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perinatal outcome, used gray scale alone. The use of colour Doppler has only recently been
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introduced. The investigations to date have all shown that using colour Doppler will lead to a reduction in the AFI or the SDP when compared to gray scale alone. This raises the question as to whether the original studies that evaluated outcomes in pregnancies estimated to have oligohydramnios need to be redone if colour Doppler is now going to be used to estimate AFV. In the only study to date which compared colour Doppler with gray scale in the diagnosis of an actual AFV by dye-determination, colour Doppler did not identify more pregnancies with actual oligohydramnios, but instead labelled normal pregnancies as having oligohydramnios resulting
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in the over diagnosis of oligohydramnios. Because preterm, near term, and even term pregnancies may undergo additional antenatal testing, labour induction and delivery based on a diagnosis of oligohydramnios, even if other assessment of fetal well-being are reassuring of fetal
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health, the accurate diagnosis of oligohydramnios is essential. If colour Doppler is to be used, it may be necessary to reduce our thresholds by 20%, the AFI from 5 to 4 and the SDP from 2 to 1.6, to categorize pregnancies as having oligohydramnios. It is uncertain whether we can rely on
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a new, largely unstudied technique, colour Doppler, to estimate AFV when that technique does not lead to the detection of more pregnancies with actual low AFVs. Only future studies that
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compare pregnancy outcomes using colour Doppler compared with gray scale can truly answer these questions.
Ultrasound Estimated AFV and Pregnancy Outcomes: Oligohydramnios
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Most of the investigations that have evaluated AFVs and pregnancy outcomes have done so using ultrasound estimates of AFV because the methods to determine true AFV involve either dye-determined volumes that are invasive, time consuming and require laboratory support, or are
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done at Caesarean delivery. Despite these limitations, there are a few studies in which the volume of fluid was determined by dye-dilution techniques and delivery occurred within 48-72
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hours of the AFV determination. One study followed the outcome of 50 singleton pregnancies with a dye-determined AFV within 48 hours of delivery [23]. The investigators noted a greater risk of Caesarean delivery for fetal intolerance of labour in the patients with polyhydramnios but no difference in risk of meconium-stained fluid, variable decelerations resulting in delivery or low 5-minute Apgar scores between the polyhydramnios, oligohydramnios and normal groups. Another study followed the outcome of 100 women with dye-determined AFV delivered by an elective or repeat Caesarean section (none of these pregnancies laboured) and noted that
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oligohydramnios was not predictive of low umbilical artery pH at time of delivery [45]. In yet a third dye-determined AFV study following 74 patients, AFV was not found to be predictive of 10 studied intrapartum and neonatal outcomes including fetal heart rate variability, variable
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decelerations, late decelerations, fetal labour intolerance, need for amnioinfusion, intrauterine growth restriction, birth weight, mode of delivery, admission to neonatal intensive care unit, or umbilical cord gas <7.2. Additionally, when the 10 adverse outcomes were evaluated, there was
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no significant difference in AFVs between the group that had the adverse outcome and the group
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that did not [46].
The classically quoted investigation of the use of an AFI < 5 compared to an AFI of > 5 to predict adverse pregnancy outcomes is the study by Rutherford et al. That group observed in 330 high risk pregnancies that those pregnancies with an AFI of < 5 compared to the pregnancies with an AFI of >5 had an increased risk of fetal heart rate decelerations in labour, meconium
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stained amniotic fluid, Caesarean deliveries for fetal distress, and lower Apgar scores [10]. Multiple studies have been undertaken to determine the correlation between an ultrasound estimated AFV that is labelled as oligohydramnios (AFI < 5) compared with an AFV that the
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ultrasound is labelled as normal (AFI 5-25). The conclusions of the studies have differed, with
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some investigations showing a strong association between an AFI < 5 and adverse pregnancy outcomes and others not showing any such association. Chauhan et al undertook a meta-analysis of studies which evaluated antepartum and intrapartum perinatal outcomes comparing an AFI > 5.0 vs. < 5.0 by evaluating the association with Caesarean delivery for fetal distress, 5 minute Apgar score < 7, and umbilical artery pH < 7.0. Eighteen studies between 1987 and 1997 were identified. There was an increased risk for Caesarean delivery for fetal distress (relative risk [RR]) = 2.2) and for 5 minute Apgar score <7
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(RR = 5.2). An intrapartum AFI < 5 was linked with an increased risk of Caesarean delivery for fetal distress (RR = 1.7) and 5 minute Apgar score < 7 (RR = 1.8). Only one of the evaluated studies reported the risk of umbilical artery pH < 7.0 and there was no significant difference
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between the group with AFI < 5 vs. > 5 (p=.16). The authors discuss the limitations of their findings, highlighting the remaining uncertainty of an association of low AFI < 5 and Caesarean delivery for fetal distress and Apgar scores < 7 at 5 minutes. The assessment that a fetal
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monitoring strip identifies developing or on-going fetal distress is subjective and Apgar scores are also subjective and could be the result of prematurity, presence of maternal narcotics at
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delivery or vigorous suctioning at delivery. It is concerning that the only truly objective evaluation, namely umbilical artery pH at the time of delivery, was not different between groups. The authors conclude that a large multicentre trial is needed to determine the benefits of using AFI in antepartum and intrapartum fetal surveillance [12].
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A follow up study [47] systematically reviewed all human studies from 1980 – 2015 and divided the studies into groups evaluating women at low risk for an adverse pregnancy outcome and women at high risk for an adverse pregnancy outcome. The adverse outcomes of interest were
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Caesarean delivery for fetal distress, 5 minute Apgar score < 7, NICU admission, low birth
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weight neonate, meconium staining of amniotic fluid, and meconium aspiration syndrome. The intent of the study was to also look at umbilical artery pH values, but the number of studies that collected this information was limited and the studies that reported umbilical artery pH used different thresholds (<7.0 <7.1 or <7.15), making the data too heterogeneous for comparison. Women with isolated ultrasound estimated oligohydramnios (low-risk pregnancies) were more likely to have an emergency Caesarean delivery for fetal distress (RR = 2.16), neonatal intensive care unit admission (RR = 1.72), and a neonate with meconium aspiration (RR = 2.83). The high
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risk group with oligohydramnios by ultrasound estimate were more likely to have a low birth weight neonate (RR= 2.38). All other comparisons did not differ significantly between groups.
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One of the most important aspects regarding AFV assessment is its potential association with pregnancy outcomes. Upon review of the literature, the number of studies is limited and the results are varied. Both of these meta-analyses are concerning because the subjective differences
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between the groups with an AFI < 5 vs. an AFI > 5 are significantly different but not when
objective outcomes are assessed. Looking at the trials that have compared an AFI of < 5 vs. > 5,
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or the few trials that have compared SDP < 2 vs. > 2, and looking at pregnancy outcomes, the prospective randomized trials are limited in number of participants and the retrospective studies are from data bases and the case control studies have their own limitations. These published studies have shown varying outcomes on the significance of a low fluid volume. There are also many variables besides AFV that may have an impact on antepartum and intrapartum outcomes,
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and to date, their assessment in many of these studies have been incomplete. Which Ultrasound Estimate, the AFI or the SDP, should be used to Identify
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Oligohydramnios
Magann et al noted that the measurements of the AFI and the SDP are not the same. The
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investigators observed that 72% of women with an AFI of 5cm or less (these women would be described as having oligohydramnios) still had an SDP measurement of greater than 2cm and would be labelled as having a normal AFV [48]. A study performed by Alfirevic et al further detailed the utility of SDP versus AFI. In this study of 500 women, use of AFI labelled 10% as having oligo whereas the use of SDP labeled only 2%. This resulted in an increase in labour inductions without any differences in outcome.
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Furthermore, the rate of Caesarean delivery was 18.8% in the AFI group versus only 13.2% in the SDP group [49].
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Magann et al undertook a prospective randomized trial comparing the use of the SDP with the AFI as the fluid component of the BPP to evaluate pregnancy outcomes. They observed that more pregnancies were labelled as having oligohydramnios with the use of the AFI (38%) vs. the
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SDP (17%), resulting in more labour inductions for oligohydramnios (AFI 30% vs. SDP 15%). However, no difference was noted in the percentage of Caesarean sections for labour intolerance,
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umbilical artery pH < 7.1 or < 7, amnioinfusions, or late or variable decelerations influencing delivery [50].
Moses et al evaluated the estimate of AFV on admission to labour and delivery as a fetal admission test to identify pregnancies at risk for poor intrapartum pregnancy outcomes. The
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investigators found that the AFI group labelled 25% of the women as having oligohydramios compared to 8% using the SDP technique. Neither test was able to identify a pregnancy at risk for a poor intraparutm pregnancy outcome. Low volumes by both tests were no better than the
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normal volumes of amniotic fluid in identifying adverse intrapartum pregnancy outcomes [51]. Chauhan et al undertook a prospective study comparing the AFI vs. the SDP as the fluid
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component along with the non-stress test in evaluating at-risk pregnancies. They observed that more pregnancies were labelled as having oligohydramnios with the AFI (17%) vs. the SDP (10%) but observed no difference in amnioinfusions, variable decelerations or late decelerations influencing delivery, Caesarean deliveries for fetal labour intolerance, umbilical artery pH < 7.1, Apgar scores < 7 at 5 minutes, or neonatal intensive care admission between the AFI and the SDP groups [52].
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These 5 studies were the five randomized controlled trials involving 3226 women with singleton pregnancies which demonstrated no evidence that one method of AFV estimation is superior to the other in the prevention of poor peripartum outcomes, including: admission to a neonatal
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intensive care unit, an umbilical artery pH of less than 7.1, the presence of meconium; an Apgar score of less than 7 at five minutes, or delivery via Caesarean. It was also noted in this review that the patients who were diagnosed with oligohydramnios by AFI measurement had a higher
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rate of caesarean section for fetal distress. The authors of the review concluded that single
deepest vertical pocket is a better measurement choice because the use of AFI increases the rate
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of diagnosis of oligohydramnios and the rate of induction of labour without improvement in peripartum outcomes [49].
Ultrasound Estimated AFV and Pregnancy Outcomes: Polyhydramnios
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The causes of polyhydramnios include idiopathic, the most common reason, follow by congenital anomalies/genetic disorders, maternal diabetes, twins, fetal anaemia, placental tumour and other, more rare, causes [53]. The identification of polyhydramnios by ultrasound is poor. In a series of
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31 women with dye-determined polyhydramnios, the predictability of the AFI and the SDP (> 95th % and 97th %) to identify polyhydramnios was between 33% and 46% [54]. The addition of
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colour Doppler, as was shown in true low volume of fluid, does not increase the detection of polyhydramnios [44].
Once the other reasons for polyhydramnios have been excluded, there are few studies that
have evaluated idiopathic polyhydramnions and pregnancy outcomes. Approximately 1-2% of all pregnancies are complicated by polyhydramnios and in about half of those pregnancies, the reason for the polyhydramnios is idiopathic [55]. In a review of pregnancies with idiopathic
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polyhydramnios compared to pregnancies with normal fluid, there is a link to fetal macrosomia, an increased risk of adverse pregnancy outcomes, and a 2-5 fold increased risk of perinatal mortality (corrected for congenital anomalies). There has been a limited number of reports on
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idiopathic polyhydramnios since that review. In a retrospective analysis of 59 pregnancies
complicated by idiopathic polyhydramnios and 101 normal controls, there were more preterm deliveries and low (< 7) 1 and 5 minute Apgar scores in the idiopathic group compared to
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controls [56]. In a case control study of perinatal outcomes in pregnancies complicated by idiopathic polyhydramnios, 500 hundred women were compared to 500 normal pregnant
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controls. There was an increased risk of preterm delivery, maternal complications, and higher perinatal mortality in the polyhydramnios group [57]. A more recent investigation evaluated the short and long term effects, in children from ages 4-9 years, of pregnancies complicated by polyhydramnios and a normal ultrasound. Women with diabetes were included, but after
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controlling diabetes, the rates of Caesarean delivery, large for gestational age, macrosomia, overall malformation rate, neonatal intensive care unit admissions, and neurodevelopmental disorders were significantly increased in the polyhydramnios group compared to a matched
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control group with normal amniotic fluid and normal ultrasound [58].
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Overall information about idiopathic polyhydramnios and pregnancy outcome is very limited. Inadequate information suggests that there is a greater risk of preterm delivery, macrosomic fetuses and overall perinatal mortality in pregnancies complicated by idiopathic polyhydramnios. The role of antenatal testing in the identification and prevention of adverse outcomes is uncertain. Future studies will be needed to help with the understanding and management of pregnancies complicated by idiopathic polyhydramnios.
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Based on our observations in our patient population since we have adopted the use of the SDP in the assessment of AFV to identify at-risk pregnancies with oligohydramnios, we suspect that, just like the AFI over diagnosed oligohydramnios leading to more interventions without an
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improvement in perinatal outcomes, the SDP of > 8 may over diagnosis polyhydramnios. We now have an ongoing study to try to determine whether the AFI or the SDP is a better ultrasound
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measurement to use in the assessment of polyhydramnios.
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Correlation of Oligohydramnios and Polyhydramnios with Pregnancy Outcomes
The complexity of the association between AFV and pregnancy outcomes is highlighted by the varying results of these studies. Several studies, such as one by Golan et al, note that the aetiology behind the abnormal fluid volumes may influence pregnancy outcomes more than the actual fluid itself. Golan et al performed a study that found that women with polyhydramnios had
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increased risk of maternal complications such as diabetes mellitus and pregnancy induced hypertension as well as obstetrical complications including preterm delivery, abnormal fetal presentation and fetal anomalies [59]. Chauhan et al also showed that knowledge of amniotic
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fluid estimate by the health care provider results in a higher number of Caesarean deliveries for
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fetal compromise during labour than if the estimation is unknown [60]. In that study, despite the increased frequency of Caesarean deliveries, there were no differences in the neonatal outcomes between the two groups as evidenced by presence of meconium, umbilical cord pH of less than 7.1, 1-minute Apgar score less than 7, or admission to neonatal intensive care unit. Summary
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The assessment and understanding of AFV is an established component of obstetrical care. The regulation of AFV is a highly dynamic process that is dependent upon fetal urination, fetal swallowing, fluid production by the fetal lung, skin and oral-nasal cavities, the intramembranous
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pathway, and the transmembranous pathway [8]. The AFV has also been shown to vary based on gestational age [30]. The ultrasound estimation of AFV is an important component of antenatal testing because, if reduced, it is suggestive of chronic in-utero stress. When combined with other
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forms of antenatal testing, it is thought to be an important indicator of fetal well-being. This is evidenced by the false negative rate of an NST alone (1.2-5/1000) versus a modified BPP
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(0.8/1000). Currently, routine use of colour Doppler to calculate AFV is not recommended as it could lead to over diagnosis of oligohydramnios and increased interventions. Based on the current literature, the use of SDP is currently recommended because use of AFI is associated with a higher rate of obstetric interventions. Pregnancy outcomes related to oligo- and
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polyhydramnios is complex and variable as has been noted in multiple studies. Further research on the topic is needed, which will continue to shape obstetrical practice regarding the
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interpretation of AFV.
Acknowledgements
Special thanks to Donna Eastham for editing and submission. Conflict of Interest: None
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Practice Points • Colour Doppler has been shown to lead to an over diagnosis of oligohydramnios when
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used to calculate the AFV and could lead to an increase in obstetric interventions. Further studies are needed before the use of colour Doppler is adopted into routine practice [44].
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• SDP should be used to determine if the AFV is low in at-risk pregnancies as the use of the AFI is associated with a higher rate of obstetric interventions (labour inductions)
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without an improvement in pregnancy outcomes [40].
• We suspect, based on observations in our own patient population and on preliminary information from an ongoing trial at our institution, that, just as the AFI over diagnoses oligohydramnios, the SDP over diagnoses polyhydramnios at an SDP of > 8. To detect
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Research Agenda
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adverse outcomes associated with polyhydramnios, the AFI may be superior to the SDP.
1. Define normal amniotic fluid volume
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2. Determine whether AFI or SDP is the best estimate of oligohydramnios 3. Review pregnancy outcomes in situations with oligohydramnios and polyhydramnios 4. Evaluate whether colour Doppler should be used in the assessment of AFV.
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References:
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1. Freeman RK, Anderson G, Dorchester W. A prospective multiinstitutional study of antepartum fetal heart rate monitoring. II. Contraction stress test versus nonstress test for primary surveillance. Am J Obstet Gynecol 1982; 143: 778–781. 2. *Manning FA, Platt LD, Sipos L. Antepartum fetal evaluation: development of a fetal biophysical profile. Am J Obstet Gynecol 1980;136(6):787-795. 3. Miller DA, Rabello YA, Paul RH. The modified biophysical profile: antepartum testing in the 1990s. Am J Obstet Gynecol 1996 Mar; 174(3):812-817. 4. Manning FA, Snijders R, Harman CR, et al. Fetal biophysical profile score. VI. Correlation with antepartum umbilical venous fetal pH. Am J Obstet Gynecol 1993; 169(4):755-63. 5. Freeman RK, Anderson G, Dorchester W. A prospective multi-institutional study of antepartum fetal heart rate monitoring; I. Risk of perinatal mortality and morbidity according to antepartum fetal heart rate results. Am J Obstet Gynecol 1982; 143:771. 6. Beall MH, van den Wijngaard JP, van Gemert MJ, Ross MG. Amniotic fluid water dynamics. Placenta 2007; 28:816-823. 7. Gitlin D, Kumate J, Morales C, et al. The turnover of amniotic fluid protein in the human conceptus. Am J Obstet Gynecol 1972; 113(5):632-645. 8. Modena AB, Fieni S. Amniotic fluid dynamics. Acta Biomed 2004; 75(suppl):11-13. 9. Magann EF, Sandlin AT, Ounpraseuth ST. Amniotic fluid and the clinical relevance of the sonographically estimated AFV. J Ultrasound Medicine 2011; 30:1573-1585. 10. *Rutherford SE, Phelan JP, Smith CV, Jacobs N. The four-quadrant assessment of AFV: an adjunct to antepartum fetal heart rate testing. Obstet Gynecol 1987; 70(3 Pt 1):353356. 11. Baron C, Morgan MA, Garite TJ. The AFV assessed intrapartum on perinatal outcome. Am J Obstet Gynecol 1995; 173:167-174. 12. Chauhan SP, Sanderson M, Hendrix NW, et al. Perinatal outcome and amniotic fluid index in the antepartum and intrapartum periods: A meta-analysis. Am J Obstet Gynecol 1999;181(6):1473-1478. 13. Horsager R, Nathan L, Leveno KJ. Correlation of measured AFV and sonographic predictions of oligohydramnios. Obstet Gynecol 1994; 83:955-958. 14. *Magann EF, Nolan TE, Hess LW, et al. Measurement of AFV: accuracy of ultrasonography techniques. Am J Obstet Gynecol 1992; 167:1533-1537. 15. Dildy GA III, Lira N, Moise KJ Jr, et al. AFV assessment: comparison of ultrasonographic estimates versus direct measurements with a dye-dilution technique in human pregnancy. Am J Obstet Gynecol 1992; 167:986-994. 16. Magann EF, Doherty DA, Chauhan SP, et al. How well do the amniotic fluid index and SDP indies (below the 3rd and 5th and above the 95th and 97th percentiles) predict oligohydramnios and hydramnios? Am J Obstet Gynecol 2004; 190:164-169. 17. Chamberlain PF, Manning FA, Morrison I, et al. Ultrasound evaluation of AFV, I: the relationship of marginal and decreased AFVs to perinatal outcomes. Am J Obstet Gynecol 1984; 150:245-249. 18. Morris JM, Thompson K, Smithey J, et al. The usefulness of ultrasound assessment of amniotic fluid in predicting adverse outcome in prolonged pregnancy: a prospective blinded observational study. BJOG 2003; 110:989-994.
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19. Magann EF, Sanderson M, Martin JN, Chauhan S. The amniotic fluid index, SDP, and two-diameter pocket in normal human pregnancy. Am J Obstet Gynecol 2000; 182:15811588. 20. Moore TR, Cayle JE. The amniotic fluid index in normal human pregnancy. Am J Obstet Gynecol 1990; 162:1168-1174. 21. Casey BM, McIntire DD, Bloom SL, et al. Pregnancy outcomes after antepartum diagnosis of oligohydramnios at or beyond 34 weeks’ gestation. Am J Obstet Gynecol 2000; 182:909-912. 22. Magann EF, Perry KG Jr, Chauhan SP, et al. The accuracy of ultrasound evaluation of AFV in singleton pregnancies: the effect of operator experience and ultrasound interpretative technique. J Clin Ultrasound 1997; 25:249-253. 23. Magann EF, Morton ML, Nolan TE, et al. Comparative efficacy of two sonographic measurements for the detection of aberrations in the AFV and the effects of AFV on pregnancy outcomes. Obstet Gynecol 1994; 83:959-962. 24. Chamberlain PF, Manning FA, Morrison I, et al. Ultrasound evaluation of AFV. II. The relationship of increased AFV of perinatal outcome. Am J Obstet Gynecol 1984; 150:250-254. 25. Carlson DE, Platt LD, Medearis AL, Horenstein J. Quantifiable polyhydramnios: diagnosis and management. Obstet Gynecol 1990; 75:989-993. 26. *Phelen JP, Ahn MO, Smith CV, et al. Amniotic fluid index measurements during pregnancy. J Reprod Med 1987; 32:601-604. 27. *Brace RA, Wolf EJ. Normal AFV changes throughout pregnancy. Am J Obstet Gynecol 1989; 161:382-388. 28. *Magann EF, Bass D, Chauhan SP, et al. AFV in normal singleton pregnancies. Obstet Gynecol 1997; 90:524-528. 29. *Queenan JT, Thompson W, Whitfield CR, Shah SI. AFVs in normal pregnancies. Am J Obstet Gynecol 1972; 114:34-38. 30. *Sandlin AT, Ounpraseuth ST, Spencer HJ, et al. AFV in normal singleton pregnancies: modeling with quantile regression. Arch Gynecol Obstet 2014; 289(5):967-972. 31. Sepulveda W, Flack NJ, Fisk NM. Direct volume measurement at midtrimester amnioinfusion in relation to ultrasonographic indexes of AFV. Am J Obstet Gynecol 1994 Apr; 170(4):1160-1163. 32. Croom CS, Banias BB, Ramos-Santos E, et al. Do semiquantitative amniotic fluid indexes reflect actual volume? Am J Obstet Gynecol 1992 Oct; 167(4 Pt 1):995-999. 33. Magann EF, Nevils BG, Chauhan SP, et al. Low AFV is poorly identified in singleton and twin pregnancies using the 2 x 2 cm pocket technique of the biophysical profile. South Med J 1999 Aug; 92(8):802-805. 34. Magann EF, Chauhan SP, Sanderson M, et al. AFV in normal pregnancy: comparison of two different normative datasets. J Obstet Gynaecol Res 2012 Feb; 38(2):364-370. 35. Horsager R, Nathan L, Leveno KJ. Correlation of measured AFV and sonographic predictions of oligohydramnios. Obstet Gynecol 1994 Jun; 83(6):955-958. 36. Magann EF, Ounpraseuth S, Chauhan SP, et al. Correlation of ultrasound estimated with dye-determined or directly measured AFV revisited. Gynecol Obstet Invest 2015; 79(1):46-49. 37. Magann EF, Chauhan SP, Barrilleaux PS, et al. Amniotic fluid index and SDP: weak indicators of abnormal amniotic volumes. Obstet Gynecol 2000 Nov; 96(5 Pt 1):737-740.
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38. Magann EF, Chauhan SP, Whitworth NS, et al. Do multiple measurements employing different ultrasonic techniques improve the accuracy of AFV assessment? Aust N Z J Obstet Gynaecol 1998 May; 38(2):172-175. 39. Magann, EF, Chauhan SP, Sanderson M, et al. AFV in normal pregnancy: Comparison of two different normative datasets. J Obstet Gynaecol Res 2012; 38(2):364-370. 40. *Nabhan AF, Abdelmoula YA. Amniotic fluid index versus single deepest vertical pocket as a screening tst for preventing adverse pregnancy outcome. Cochrane Database Syst Rev 2008; 3:CD006593. 41. *Phelan JP, Smith CV, Broussard P, Small M. AFV assessment with the four-quadrant technique at 36-42 weeks' gestation. J Reprod Med 1987 Jul; 32(7):540-542. 42. Bianco A, Rosen T, Kuczynski E, et al. Measurement of the amniotic fluid index with and without colour Doppler. J Perinat Med 1999; 27(4):245-9. 43. Goldkrand JW, Hough TM, Lentz SU, et al. Comparison of the amniotic fluid index with gray-scale and colour Doppler ultrasound. J Matern Fetal Neonatal Med 2003 May; 13(5):318-322. 44. Magann EF, Chauhan SP, Barrilleaux PS, et al. Ultrasound estimate of AFV: colour Doppler overdiagnosis of oligohydramnios. Obstet Gynecol 2001 Jul; 98(1):71-4. 45. Magann EF, Chauan Sp, Martin JN Jr. Is AFV status predictive of fetal acidosis at delivery? Aust NZ J Obstet Gynaecol 2003; 43:129-133. 46. Magann EF, Doherty DA, Chauhan SP, Lanneau GS, Morrison JC. Dye-determined AFV and intrapartum/neonatal outcome. J Perinatol 2004; 24:423-428. 47. Rabie N, Magann E, Steelman S, Ounpraseuth S. Oligohydramnios in complicated and uncomplicated pregnancies: a systematic review and meta-analysis.Ultrasound Obstet Gynecol. 2016 Apr 7 48. Magann EF, Chauhan SP, Kinsella MJ, et al. Antenatal testing among 1001 patient at high risk: the role of ultrasonographic estimate of AFV. Am J Obstet Gynecol 1999; 180:1330-1336. 49. Alfirevic Z, Luckas M, Walkinshaw SA, et al. A randomized comparison between amniotic fluid index and maximum pool depth in monitoring of post-term pregnancy. Br J Obstet Gynaecol 1997; 104:207-211. 50. Magann EF, Doherty DA, Field K, et al. Biophysical profile with AFV assessments. Obstet Gynecol 2004; 104:5-10. 51. Moses J, Doherty DA, Magann EF, et al. A randomized clinical trial of the intrapartum assessment of AFV: Amniotic fluid index versus the SDP technique. Am J Obstet Gynecol 2004; 190:1564-1570. 52. Chauhan SP, Doherty DA, Magann EF, et al. Amniotic fluid index vs SDP technique during modified biophysical profile: A randomized clinical trial. Am J Obstet Gynecol 2004; 191:661-668. 53. Sandlin AT, Chauhan SP, Magann EF. Clinical relevance of sonographically estimated AFV: polyhydramnios. J Ultrasound Med 2013; 32(5):851-863. 54. Magann EF, Doherty DA, Chauhan SP, et al. How well do the amniotic fluid index and SDP indices (below the 3rd and 5th and above the 95th and 97th percentiles) predict oligohydramnios and hydramnios? Am J Obstet Gynecol 2004; 190:164-169. 55. Magann EF, Chauhan SP, Doherty DA, et al. A review of idiopathic hydramnios and pregnancy outcomes. Obstet Gynecol Surv 2007; 62:795-802.
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56. Taskin S, Pabuccu EG, Kanmaz AG, Kurtay G. Perinatal outcomes of idiopathic polyhydramnios. Interv Med Appl Sci 2013; 5:21-25. 57. Lallar M, Anam UI Hag, Nandal R. Perinatal outcome in idiopathic polyhydramnios. J Obstet Gynaecol India 2015; 65:310-314. 58. Yefet E, Daniel-Spiegel E. Outcomes from polyhydramnios with normal ultrasound. Pediatrics 2016; 137(2):peds.2015-1948. 59. Golan A, Wolman I, Sagi J, et al. Persistence of polyhydramnios during pregnancy—its significance and correlation with maternal and fetal complications. Gynecol Ovstet Invest 1994; 37(1):18-20. 60. Chauhan SP, Washburne JF, Magann EF, et al. A randomized study to assess the efficacy of the amniotic fluid index as a fetal admission test. Obstet Gynecol 1995: 86(1):9-13.
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Figure 1: Studies that have defined Normal AFV across Gestation Figure 2: AFV assessment with and without Colour Doppler Table 1: Antenatal surveillance tests and their false negative rate
False Negative Rate .4/1000 .6//1000 .8/1000 1.9-5/1000
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Test Contraction Stress Test Biophysical Profile CTG and AFV Estimate CTG only
Table 2: Table of Studies Correlating AFI and SDP
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Measurement Sensitivity to detect AFI/SDP oligohydramnios Magann 33 AFI 6.7% Magann 34 AFI 8.7% Horsager 35 AFI 18% Magann 36 SDP 14% Magann 37 AFI / SDP 10% / 5% AFI = Amniotic Fluid Index; SDP = Single Deepest Pocket
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Study
2000
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Brace & Wolf
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Magann
max at week 34
Queenan
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Amniotic Fluid Volume (mL)
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1000
Sandlin
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max at week 38
max at week 33
100
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max at week 40
16
18
20
22
24
26
28
30
Gestational Age (wks)
32
34
36
38
40
42
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•
Amniotic fluid volume is critical in the assessment of high risk pregnancies
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Ultrasound estimates of amniotic fluid volume accurately predict normal fluid volumes but inadequately predict abnormal amniotic fluid volumes (oligohydramnios and polyhydramnios) Amniotic fluid Index over diagnoses oligohydramnios leading to more labor inductions without
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improving perinatal outcome
Colour Doppler does not improve the accuracy of identifying actual oligohydramnios
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Single deepest pocket is a better measurement than the amniotic fluid Index in diagnosing
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•
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oligohydramnios
PII:
S1521-6934(16)30077-3
DOI:
10.1016/j.bpobgyn.2016.08.004
Reference:
YBEOG 1636
To appear in:
Best Practice & Research Clinical Obstetrics & Gynaecology
Received Date: 1 April 2016 Revised Date:
10 June 2016
Accepted Date: 8 August 2016
Please cite this article as: Hughes DS, Magann EF, Antenatal Fetal Surveillance “Assessment of the AFV”, Best Practice & Research Clinical Obstetrics & Gynaecology (2016), doi: 10.1016/ j.bpobgyn.2016.08.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Antenatal Fetal Surveillance “Assessment of the AFV”
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Dawn S. Hughes, MD; Everett F. Magann, MD Department of Obstetrics and Gynecology, University of Arkansas for Medical Sciences, Little Rock, AR, USA Corresponding author: Everett F. Magann, MD
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Department of Obstetrics & Gynecology, UAMS 4301 W. Markham St. Slot # 518, Little Rock, AR 72205, USA
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Phone: 001-501-686-8345; Fax: 001-501-526-7820; Email: [email protected]
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ABSTRACT The evaluation of AFV is an established part of the antenatal surveillance of pregnancies at risk
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for an adverse pregnancy outcome. The two most commonly used ultrasound techniques to
estimate AFV are the amniotic fluid index (AFI) and the single deepest pocket (SDP). Four
studies have defined normal AFVs and, although their normal volumes have similarities, there
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are also differences primarily due to the statistical methodology used in each study. Dye-
determined AFV correlates with ultrasound estimates for normal fluid volumes but correlates
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poorly for oligohydramnios and polyhydramnios. The addition of colour Doppler in estimating AFV leads to the over diagnosis of oligohydramnios. Neither the AFI nor the SDP is superior in identifying oligohydramnios, but the SDP is a better measurement choice as the use of AFI increases the diagnosis rate of oligohydramnios and labour inductions without an improvement
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in pregnancy outcomes.
KEYWORDS: AFV; Oligohydramnios; Polyhydramnios; Pregnancy
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Introduction
The assessment of amniotic fluid volume (AFV) is an established part of the antenatal fetal
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surveillance of a pregnancy at risk for an adverse pregnancy outcome. The gold standard for antenatal surveillance for many US-based investigators is the contraction stress test (CST), which has a false negative rate of .4/1000. However, because of the necessity to have either spontaneous contractions or to start an intravenous line and induce contractions with oxytocin and the high false positive results, this test is less frequently used today [1]. Currently, two commonly used antenatal tests are the BPP (biophysical profile) and the modified BPP. The
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components of the BPP include non-stress test or cardiotocography, fetal breathing, fetal movement, fetal tone and AFV assessment. [2] The components of the modified BPP include non-stress test or cardiotocography and AFV assessment. [3] Both tests estimate the AFV by
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ultrasound as an essential component of the antenatal test. Both tests have good reliability with a false negative rate of .6/1000 for the BPP and a false negative rate of .8/1000 for the modified BPP [4]. The significance of estimating the AFV is underscored with the modified BPP. The
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false negative rate is observed to increase to 1.9-5/1000 when the non-stress
test/cardiotocography is done as a stand-alone test without an estimation of the AFV [5]. (Table
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1) The CST is able to identify both acute and chronic stress by the presence of repetitive late decelerations, whereas the BPP can only identify acute stress. The modified BPP is able to identify both acute and chronic stress by the addition of the AFV measurement. It is believed that the fetus under chronic stress will shunt blood to the brain, heart, and adrenal glands at the
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expense of other bodily organs. This shunting of blood away from the kidneys results in decreased renal perfusion and, consequently, to decreased fetal urinary output. This ultimately causes a decrease in the AFV. Therefore, the estimation of AFV by ultrasound is believed to aid
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in the recognition of the fetus under chronic stress that results from utero-placental insufficiency.
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The Pathophysiology of Amniotic Fluid
Amniotic fluid provides a supportive and protective environment for fetal development during gestation by protecting the fetus from trauma, possessing bacteriostatic properties, allowing for fetal movement and thus fostering development of the limbs and lungs and preventing compression of the umbilical cord [6]. The dynamics of the regulation of AFV are complex, with the entire volume of AF turning over on a daily basis [7]. The production and resorption of AFV is influenced by several sources, including fetal urination, fetal swallowing, fluid production by
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the fetal lung, skin and oral-nasal cavities, the intramembranous pathway, and the transmembranous pathway [8]. Fetal urine production is the main contributor to AFV in the
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second half of pregnancy [9]. What is Normal Amniotic Fluid Volume?
It is important to clearly define what a normal AFV is in order to then identify what is abnormal.
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The definition is an important one because it impacts pregnancy management. Multiple studies have shown that low abnormalities of AFV (oligohydramnios) have been associated with adverse
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pregnancy outcomes [10, 11, 12]. Multiple definitions of what constitutes an abnormal AFV can be found in the literature [9]. Oligohydramnios, or low AFV, has been defined as less than 200 mL [13], less than 500 mL total volume [14,15], less than the 5th percentile for gestational age [16], as SDP less than 2cm [17, 18, 19], an AFI of less than 5 cm [10, 11, 19, 20, 21], or an AFV
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that is subjectively low [22]. Polyhydramnios, or an increased AFV, has been defined as a total volume that is greater than 2000 mL [23], an AFV that is greater than the 95th percentile for gestational age [20], an SDP of greater than 8 cm [24], an AFI of greater than 24 cm [25] or
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greater than 25 cm [26], or an AFV that is subjectively increased [22]. There are 4 studies which have defined normal AFV across gestation. Brace et al. derived
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from the literature normal volumes using dye-dilution techniques and direct measurements at the time of hysterotomy of 705 pregnancies without fetal anomalies, maternal or fetal disease, fetal death, or spontaneous abortion [27]. The investigators observed that the AFV did not change significantly between 22 and 39 weeks. The AFV peaked between 33 to 34 weeks with a subsequent decline thereafter. Magann et al evaluated 144 normal pregnancies in a singleton institution using dye-dilution techniques to create a growth curve of normal pregnancies across
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gestation. The investigators observed that the AFV continued to increase during gestation, peaking at 40 weeks [28]. Queenan et al. also used dye-dilution techniques to assess 172 patients between 15 to 42 weeks and observed a peak of AFV at 33 to 34 weeks with a decline thereafter
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[29]. Sandlin et al evaluated 379 normal pregnancies from 16-41 weeks (144 of these
pregnancies had been previously reported by Magann [28]) using both dye-dilution techniques and direct measurement at the time of Caesarean section and used modelling by quantile
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regression to create a normative chart of AFV across gestation with a peak at 38 weeks [30]. There are similarities but also differences in their normal volumes across gestation primarily due
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to the statistical methods used. (Figure 1) As evidenced by these studies, there is not yet a clearly defined value for a “normal” AFV. What should define normal is a value that is neither excessively high nor low; what should drive the definition of abnormal is poor clinical outcomes associated with such measurements.
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Correlation of Dye-Determined or Directly Measured AFV to Ultrasound Estimates of Amniotic Fluid Volume
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There have been a number of investigations that have correlated the ultrasound estimate of AFV to a true volume of amniotic fluid (dye determined or directly measured at the time of Caesarean
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section). In a study of 5 near term sheep presented as an abstract at the Society of Gynecological Investigation in 1988, the amniotic and allantoic fluid was drained from the sheep and the uteri were filled with 2 to 2.5 liters of normal saline. At each 100 ml infusion of saline, an AFI was done. Using curve fitting formulas, there was good correlation between the increasing AFI and the amount of saline infused (r=0.94). Unfortunately, in a study by Sepulveda in 16 pregnancies with mid-gestation oligohydramnios, the correlation of the infused saline with an increasing AFI was not as good [31]. These women underwent amniocentesis with infusions of saline and
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ultrasound estimates of AFV using the SDP and AFI. It was observed that only 30% of the variation of the ultrasounds could be explained by the saline infusion. Croom et al correlated AFI and SDP with dye-determined volumes of 50 women undergoing Caesarean deliveries and found
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good correlation but only 2 pregnancies had oligohydramnios and none had polyhydramnios [32]. Dildy et al, correlating the ultrasound measurements with dye-determined fluid AFV,
observed that the AFI overestimated AFV by 89% at low volumes and by 54% at high volumes
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[15]. Magann et al in 2 studies showed that the correlation of the AFI with normal fluid was good, but when the AFV was low, the sensitivity of the AFI to detect oligohydramnios was only
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6.7% in one study and 8.7% in the second study [33, 34]. Horsager et al observed, in a study that correlated ultrasound estimate with directly measured AFV at the time of Caesarean delivery, that the sensitivity of the AFI to detect directly measured oligohydramnios was only 18% [35]. Magann, in a study of the SDP to detect oligohydramnios, observed that only 14% of the dye-
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determined oligohydramnios pregnancies were identified by using the SDP technique [36]. In the largest study correlating the SDP and AFI with dye determined AFV, both the AFI (sensitivity 10% and specificity 96%) and the SDP (sensitivity 5% and specificity 98%) were unreliable in
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identifying oligohydramnios [37]. These studies consistently document that the ultrasound estimate of AFV correlates well with normal dye-determined or directly measured AFVs but
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poorly with true volumes of abnormal fluid volumes (oligohydramnios and polyhydramnios). Magann et al has also shown that the accuracy of determining normal AFV was not improved by combining commonly used US techniques including AFI, SDP, 2-diameter pocket technique and subjective assessment [38]. It was also noted that simple subjective assessment of AFV by a trained sonographer appears to be just as accurate as the more complex ultrasonic measurements of determining abnormal AFVs.[22] (Table 2)
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Two investigations have compared the normative datasets of Brace et al [27] and Magann et al [28] in the detection of low, normal, and polyhydramnios using fixed cut offs stratified by gestational age and in the correlation of AFI and the SDP to the modelled growth curves. In the
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first study, the fixed cut offs of AFV of < 500 ml was classified as oligohydramnios, 500-2000 ml as normal AFV and > 2000 ml as polyhydramnios [39]. The study found that Brace and Magann databases classified the AFVs differently 24% of the time. The Brace dataset classified
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19% of the volumes as oligohydramnios, 71% as normal AFV, and 10% as polyhydramnios. On the other hand, the Magann dataset classified 3% as oligohydramnios, 83% as normal AFV and
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14% as having polyhydramnios. The authors concluded that the two datasets were not exchangeable and that abnormal volumes cannot be clearly identified until normal volumes are defined. An investigation that assessed the correlation between the AFI and SDP techniques with the AFV as modelled by normal curves of Brace and Magann revealed that, overall, there
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was good correlation between the AFI and SDP and the actual volumes of both Brace [27] and Magann [28] [36]. The AFI normal ranges of 5.1 - 20 versus 5.1 - 24 was better correlated with the normal volumes of both Brace and Magann. The AFI and SDP better predict
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oligohydramnios using the Brace model, while the Magann model more accurately predicts normal AFV and polyhydramnios. The authors suggested that future investigations would need
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to focus on emerging statistical methodologies to create normal curves which will be better able to define abnormal AFVs.
Estimate of AFV using Ultrasound
While measurement of AFV using dye-dilution techniques or direct measurement at time of Caesarean delivery are the most accurate methods to determine the actual AFV, these methods are invasive, labour-intensive, and the measurement technique can only be done at the time of
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Caesarean delivery. Therefore, AFV is frequently estimated using ultrasonography [40]. The two techniques most frequently used to measure AFV are the AFI and the SDP. The AFI is calculated by the operator first dividing the uterine cavity into four quadrants, and then measuring the fluid
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pocket with the largest vertical diameter within each quadrant. Each pocket must have a
horizontal diameter of at least 1 cm, and the operator must keep the transducer perpendicular to the floor and not the uterine contour. Measurement of a pocket in which there is the brief
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appearance of the umbilical cord is acceptable, but if it remains in the pocket, then another
pocket should be measured. The sum of these four measurements is then calculated to determine
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the AFI [41]. An AFI of <5 is defined as oligohydramnios, 5-24 or 25 as normal and > 24 or 25 as polyhydramnios. The SDP is calculated by measuring the vertical dimension of the largest pocket of amniotic fluid that does not contain umbilical cord or fetal extremities with a horizontal measurement of at least 1 cm. It is also important that the SDP is measured at a right
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angle to the floor and not the uterine contour. An SDP of < 2 is classified as oligohydramnios, 28 as normal, and >8 as polyhydramnios [2].
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Should the Ultrasound Estimate of AFV Be Done with Colour Doppler or Gray Scale? The initial assessments to estimate the AFV, the SDP of the BPP, and the AFI of the modified
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BPP were done using gray scale assessment. If there were multiple loops of cord, or if there were small parts in the pocket, then that pocket of fluid was not measured. Colour Doppler has recently been used to assist in the identification of amniotic fluid pockets containing umbilical cord that may not be seen with gray scale imaging alone. It was felt important to identify pockets with umbilical cord in them that may not have been seen with gray scale imaging alone because those pockets would have been excluded from measurement based on the original methods using gray scale alone. The better detection of pockets containing umbilical cord using colour Doppler,
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it was thought, would be a better identifier of oligohydramnios (Figure 2). In a study by Bianco et al., the use of colour Doppler compared to gray scale significantly decreased the AFI and increased the number of pregnancies classified as having oligohydramnios [42]. In another study
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by Goldkrand et al., the investigators also observed that the AFI was less with Colour Doppler compared to gray scale [43]. Magann et al. observed that the AFI was reduced by approximately 20% when colour Doppler was compared to gray scale [44]. The investigators evaluated 67
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women to determine if the use of colour Doppler increased the detection of dye-determined oligohydramnios, normal AFV, and polyhydramnios. The use of colour Doppler compared to
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gray scale increased the proportion of women classified as having oligohydramnios. However, the use of colour Doppler did not accurately identify any more women with actual dyedetermined oligohydramnios, but instead labelled 9 additional women with normal dyedetermined AFV as having oligohydramnios. The authors concluded that the use of colour
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Doppler leads to the over diagnosis of oligohydramnios [44].
Most of the original investigations that set the thresholds of an AFI of <5 or an SDP of < 2 to categorize a pregnancy as having oligohydramnios, and potentially at-risk for an adverse
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perinatal outcome, used gray scale alone. The use of colour Doppler has only recently been
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introduced. The investigations to date have all shown that using colour Doppler will lead to a reduction in the AFI or the SDP when compared to gray scale alone. This raises the question as to whether the original studies that evaluated outcomes in pregnancies estimated to have oligohydramnios need to be redone if colour Doppler is now going to be used to estimate AFV. In the only study to date which compared colour Doppler with gray scale in the diagnosis of an actual AFV by dye-determination, colour Doppler did not identify more pregnancies with actual oligohydramnios, but instead labelled normal pregnancies as having oligohydramnios resulting
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in the over diagnosis of oligohydramnios. Because preterm, near term, and even term pregnancies may undergo additional antenatal testing, labour induction and delivery based on a diagnosis of oligohydramnios, even if other assessment of fetal well-being are reassuring of fetal
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health, the accurate diagnosis of oligohydramnios is essential. If colour Doppler is to be used, it may be necessary to reduce our thresholds by 20%, the AFI from 5 to 4 and the SDP from 2 to 1.6, to categorize pregnancies as having oligohydramnios. It is uncertain whether we can rely on
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a new, largely unstudied technique, colour Doppler, to estimate AFV when that technique does not lead to the detection of more pregnancies with actual low AFVs. Only future studies that
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compare pregnancy outcomes using colour Doppler compared with gray scale can truly answer these questions.
Ultrasound Estimated AFV and Pregnancy Outcomes: Oligohydramnios
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Most of the investigations that have evaluated AFVs and pregnancy outcomes have done so using ultrasound estimates of AFV because the methods to determine true AFV involve either dye-determined volumes that are invasive, time consuming and require laboratory support, or are
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done at Caesarean delivery. Despite these limitations, there are a few studies in which the volume of fluid was determined by dye-dilution techniques and delivery occurred within 48-72
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hours of the AFV determination. One study followed the outcome of 50 singleton pregnancies with a dye-determined AFV within 48 hours of delivery [23]. The investigators noted a greater risk of Caesarean delivery for fetal intolerance of labour in the patients with polyhydramnios but no difference in risk of meconium-stained fluid, variable decelerations resulting in delivery or low 5-minute Apgar scores between the polyhydramnios, oligohydramnios and normal groups. Another study followed the outcome of 100 women with dye-determined AFV delivered by an elective or repeat Caesarean section (none of these pregnancies laboured) and noted that
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oligohydramnios was not predictive of low umbilical artery pH at time of delivery [45]. In yet a third dye-determined AFV study following 74 patients, AFV was not found to be predictive of 10 studied intrapartum and neonatal outcomes including fetal heart rate variability, variable
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decelerations, late decelerations, fetal labour intolerance, need for amnioinfusion, intrauterine growth restriction, birth weight, mode of delivery, admission to neonatal intensive care unit, or umbilical cord gas <7.2. Additionally, when the 10 adverse outcomes were evaluated, there was
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no significant difference in AFVs between the group that had the adverse outcome and the group
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that did not [46].
The classically quoted investigation of the use of an AFI < 5 compared to an AFI of > 5 to predict adverse pregnancy outcomes is the study by Rutherford et al. That group observed in 330 high risk pregnancies that those pregnancies with an AFI of < 5 compared to the pregnancies with an AFI of >5 had an increased risk of fetal heart rate decelerations in labour, meconium
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stained amniotic fluid, Caesarean deliveries for fetal distress, and lower Apgar scores [10]. Multiple studies have been undertaken to determine the correlation between an ultrasound estimated AFV that is labelled as oligohydramnios (AFI < 5) compared with an AFV that the
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ultrasound is labelled as normal (AFI 5-25). The conclusions of the studies have differed, with
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some investigations showing a strong association between an AFI < 5 and adverse pregnancy outcomes and others not showing any such association. Chauhan et al undertook a meta-analysis of studies which evaluated antepartum and intrapartum perinatal outcomes comparing an AFI > 5.0 vs. < 5.0 by evaluating the association with Caesarean delivery for fetal distress, 5 minute Apgar score < 7, and umbilical artery pH < 7.0. Eighteen studies between 1987 and 1997 were identified. There was an increased risk for Caesarean delivery for fetal distress (relative risk [RR]) = 2.2) and for 5 minute Apgar score <7
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(RR = 5.2). An intrapartum AFI < 5 was linked with an increased risk of Caesarean delivery for fetal distress (RR = 1.7) and 5 minute Apgar score < 7 (RR = 1.8). Only one of the evaluated studies reported the risk of umbilical artery pH < 7.0 and there was no significant difference
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between the group with AFI < 5 vs. > 5 (p=.16). The authors discuss the limitations of their findings, highlighting the remaining uncertainty of an association of low AFI < 5 and Caesarean delivery for fetal distress and Apgar scores < 7 at 5 minutes. The assessment that a fetal
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monitoring strip identifies developing or on-going fetal distress is subjective and Apgar scores are also subjective and could be the result of prematurity, presence of maternal narcotics at
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delivery or vigorous suctioning at delivery. It is concerning that the only truly objective evaluation, namely umbilical artery pH at the time of delivery, was not different between groups. The authors conclude that a large multicentre trial is needed to determine the benefits of using AFI in antepartum and intrapartum fetal surveillance [12].
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A follow up study [47] systematically reviewed all human studies from 1980 – 2015 and divided the studies into groups evaluating women at low risk for an adverse pregnancy outcome and women at high risk for an adverse pregnancy outcome. The adverse outcomes of interest were
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Caesarean delivery for fetal distress, 5 minute Apgar score < 7, NICU admission, low birth
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weight neonate, meconium staining of amniotic fluid, and meconium aspiration syndrome. The intent of the study was to also look at umbilical artery pH values, but the number of studies that collected this information was limited and the studies that reported umbilical artery pH used different thresholds (<7.0 <7.1 or <7.15), making the data too heterogeneous for comparison. Women with isolated ultrasound estimated oligohydramnios (low-risk pregnancies) were more likely to have an emergency Caesarean delivery for fetal distress (RR = 2.16), neonatal intensive care unit admission (RR = 1.72), and a neonate with meconium aspiration (RR = 2.83). The high
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risk group with oligohydramnios by ultrasound estimate were more likely to have a low birth weight neonate (RR= 2.38). All other comparisons did not differ significantly between groups.
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One of the most important aspects regarding AFV assessment is its potential association with pregnancy outcomes. Upon review of the literature, the number of studies is limited and the results are varied. Both of these meta-analyses are concerning because the subjective differences
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between the groups with an AFI < 5 vs. an AFI > 5 are significantly different but not when
objective outcomes are assessed. Looking at the trials that have compared an AFI of < 5 vs. > 5,
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or the few trials that have compared SDP < 2 vs. > 2, and looking at pregnancy outcomes, the prospective randomized trials are limited in number of participants and the retrospective studies are from data bases and the case control studies have their own limitations. These published studies have shown varying outcomes on the significance of a low fluid volume. There are also many variables besides AFV that may have an impact on antepartum and intrapartum outcomes,
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and to date, their assessment in many of these studies have been incomplete. Which Ultrasound Estimate, the AFI or the SDP, should be used to Identify
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Oligohydramnios
Magann et al noted that the measurements of the AFI and the SDP are not the same. The
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investigators observed that 72% of women with an AFI of 5cm or less (these women would be described as having oligohydramnios) still had an SDP measurement of greater than 2cm and would be labelled as having a normal AFV [48]. A study performed by Alfirevic et al further detailed the utility of SDP versus AFI. In this study of 500 women, use of AFI labelled 10% as having oligo whereas the use of SDP labeled only 2%. This resulted in an increase in labour inductions without any differences in outcome.
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Furthermore, the rate of Caesarean delivery was 18.8% in the AFI group versus only 13.2% in the SDP group [49].
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Magann et al undertook a prospective randomized trial comparing the use of the SDP with the AFI as the fluid component of the BPP to evaluate pregnancy outcomes. They observed that more pregnancies were labelled as having oligohydramnios with the use of the AFI (38%) vs. the
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SDP (17%), resulting in more labour inductions for oligohydramnios (AFI 30% vs. SDP 15%). However, no difference was noted in the percentage of Caesarean sections for labour intolerance,
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umbilical artery pH < 7.1 or < 7, amnioinfusions, or late or variable decelerations influencing delivery [50].
Moses et al evaluated the estimate of AFV on admission to labour and delivery as a fetal admission test to identify pregnancies at risk for poor intrapartum pregnancy outcomes. The
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investigators found that the AFI group labelled 25% of the women as having oligohydramios compared to 8% using the SDP technique. Neither test was able to identify a pregnancy at risk for a poor intraparutm pregnancy outcome. Low volumes by both tests were no better than the
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normal volumes of amniotic fluid in identifying adverse intrapartum pregnancy outcomes [51]. Chauhan et al undertook a prospective study comparing the AFI vs. the SDP as the fluid
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component along with the non-stress test in evaluating at-risk pregnancies. They observed that more pregnancies were labelled as having oligohydramnios with the AFI (17%) vs. the SDP (10%) but observed no difference in amnioinfusions, variable decelerations or late decelerations influencing delivery, Caesarean deliveries for fetal labour intolerance, umbilical artery pH < 7.1, Apgar scores < 7 at 5 minutes, or neonatal intensive care admission between the AFI and the SDP groups [52].
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These 5 studies were the five randomized controlled trials involving 3226 women with singleton pregnancies which demonstrated no evidence that one method of AFV estimation is superior to the other in the prevention of poor peripartum outcomes, including: admission to a neonatal
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intensive care unit, an umbilical artery pH of less than 7.1, the presence of meconium; an Apgar score of less than 7 at five minutes, or delivery via Caesarean. It was also noted in this review that the patients who were diagnosed with oligohydramnios by AFI measurement had a higher
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rate of caesarean section for fetal distress. The authors of the review concluded that single
deepest vertical pocket is a better measurement choice because the use of AFI increases the rate
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of diagnosis of oligohydramnios and the rate of induction of labour without improvement in peripartum outcomes [49].
Ultrasound Estimated AFV and Pregnancy Outcomes: Polyhydramnios
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The causes of polyhydramnios include idiopathic, the most common reason, follow by congenital anomalies/genetic disorders, maternal diabetes, twins, fetal anaemia, placental tumour and other, more rare, causes [53]. The identification of polyhydramnios by ultrasound is poor. In a series of
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31 women with dye-determined polyhydramnios, the predictability of the AFI and the SDP (> 95th % and 97th %) to identify polyhydramnios was between 33% and 46% [54]. The addition of
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colour Doppler, as was shown in true low volume of fluid, does not increase the detection of polyhydramnios [44].
Once the other reasons for polyhydramnios have been excluded, there are few studies that
have evaluated idiopathic polyhydramnions and pregnancy outcomes. Approximately 1-2% of all pregnancies are complicated by polyhydramnios and in about half of those pregnancies, the reason for the polyhydramnios is idiopathic [55]. In a review of pregnancies with idiopathic
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polyhydramnios compared to pregnancies with normal fluid, there is a link to fetal macrosomia, an increased risk of adverse pregnancy outcomes, and a 2-5 fold increased risk of perinatal mortality (corrected for congenital anomalies). There has been a limited number of reports on
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idiopathic polyhydramnios since that review. In a retrospective analysis of 59 pregnancies
complicated by idiopathic polyhydramnios and 101 normal controls, there were more preterm deliveries and low (< 7) 1 and 5 minute Apgar scores in the idiopathic group compared to
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controls [56]. In a case control study of perinatal outcomes in pregnancies complicated by idiopathic polyhydramnios, 500 hundred women were compared to 500 normal pregnant
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controls. There was an increased risk of preterm delivery, maternal complications, and higher perinatal mortality in the polyhydramnios group [57]. A more recent investigation evaluated the short and long term effects, in children from ages 4-9 years, of pregnancies complicated by polyhydramnios and a normal ultrasound. Women with diabetes were included, but after
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controlling diabetes, the rates of Caesarean delivery, large for gestational age, macrosomia, overall malformation rate, neonatal intensive care unit admissions, and neurodevelopmental disorders were significantly increased in the polyhydramnios group compared to a matched
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control group with normal amniotic fluid and normal ultrasound [58].
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Overall information about idiopathic polyhydramnios and pregnancy outcome is very limited. Inadequate information suggests that there is a greater risk of preterm delivery, macrosomic fetuses and overall perinatal mortality in pregnancies complicated by idiopathic polyhydramnios. The role of antenatal testing in the identification and prevention of adverse outcomes is uncertain. Future studies will be needed to help with the understanding and management of pregnancies complicated by idiopathic polyhydramnios.
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Based on our observations in our patient population since we have adopted the use of the SDP in the assessment of AFV to identify at-risk pregnancies with oligohydramnios, we suspect that, just like the AFI over diagnosed oligohydramnios leading to more interventions without an
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improvement in perinatal outcomes, the SDP of > 8 may over diagnosis polyhydramnios. We now have an ongoing study to try to determine whether the AFI or the SDP is a better ultrasound
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measurement to use in the assessment of polyhydramnios.
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Correlation of Oligohydramnios and Polyhydramnios with Pregnancy Outcomes
The complexity of the association between AFV and pregnancy outcomes is highlighted by the varying results of these studies. Several studies, such as one by Golan et al, note that the aetiology behind the abnormal fluid volumes may influence pregnancy outcomes more than the actual fluid itself. Golan et al performed a study that found that women with polyhydramnios had
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increased risk of maternal complications such as diabetes mellitus and pregnancy induced hypertension as well as obstetrical complications including preterm delivery, abnormal fetal presentation and fetal anomalies [59]. Chauhan et al also showed that knowledge of amniotic
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fluid estimate by the health care provider results in a higher number of Caesarean deliveries for
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fetal compromise during labour than if the estimation is unknown [60]. In that study, despite the increased frequency of Caesarean deliveries, there were no differences in the neonatal outcomes between the two groups as evidenced by presence of meconium, umbilical cord pH of less than 7.1, 1-minute Apgar score less than 7, or admission to neonatal intensive care unit. Summary
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The assessment and understanding of AFV is an established component of obstetrical care. The regulation of AFV is a highly dynamic process that is dependent upon fetal urination, fetal swallowing, fluid production by the fetal lung, skin and oral-nasal cavities, the intramembranous
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pathway, and the transmembranous pathway [8]. The AFV has also been shown to vary based on gestational age [30]. The ultrasound estimation of AFV is an important component of antenatal testing because, if reduced, it is suggestive of chronic in-utero stress. When combined with other
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forms of antenatal testing, it is thought to be an important indicator of fetal well-being. This is evidenced by the false negative rate of an NST alone (1.2-5/1000) versus a modified BPP
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(0.8/1000). Currently, routine use of colour Doppler to calculate AFV is not recommended as it could lead to over diagnosis of oligohydramnios and increased interventions. Based on the current literature, the use of SDP is currently recommended because use of AFI is associated with a higher rate of obstetric interventions. Pregnancy outcomes related to oligo- and
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polyhydramnios is complex and variable as has been noted in multiple studies. Further research on the topic is needed, which will continue to shape obstetrical practice regarding the
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interpretation of AFV.
Acknowledgements
Special thanks to Donna Eastham for editing and submission. Conflict of Interest: None
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Practice Points • Colour Doppler has been shown to lead to an over diagnosis of oligohydramnios when
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used to calculate the AFV and could lead to an increase in obstetric interventions. Further studies are needed before the use of colour Doppler is adopted into routine practice [44].
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• SDP should be used to determine if the AFV is low in at-risk pregnancies as the use of the AFI is associated with a higher rate of obstetric interventions (labour inductions)
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without an improvement in pregnancy outcomes [40].
• We suspect, based on observations in our own patient population and on preliminary information from an ongoing trial at our institution, that, just as the AFI over diagnoses oligohydramnios, the SDP over diagnoses polyhydramnios at an SDP of > 8. To detect
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Research Agenda
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adverse outcomes associated with polyhydramnios, the AFI may be superior to the SDP.
1. Define normal amniotic fluid volume
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2. Determine whether AFI or SDP is the best estimate of oligohydramnios 3. Review pregnancy outcomes in situations with oligohydramnios and polyhydramnios 4. Evaluate whether colour Doppler should be used in the assessment of AFV.
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38. Magann EF, Chauhan SP, Whitworth NS, et al. Do multiple measurements employing different ultrasonic techniques improve the accuracy of AFV assessment? Aust N Z J Obstet Gynaecol 1998 May; 38(2):172-175. 39. Magann, EF, Chauhan SP, Sanderson M, et al. AFV in normal pregnancy: Comparison of two different normative datasets. J Obstet Gynaecol Res 2012; 38(2):364-370. 40. *Nabhan AF, Abdelmoula YA. Amniotic fluid index versus single deepest vertical pocket as a screening tst for preventing adverse pregnancy outcome. Cochrane Database Syst Rev 2008; 3:CD006593. 41. *Phelan JP, Smith CV, Broussard P, Small M. AFV assessment with the four-quadrant technique at 36-42 weeks' gestation. J Reprod Med 1987 Jul; 32(7):540-542. 42. Bianco A, Rosen T, Kuczynski E, et al. Measurement of the amniotic fluid index with and without colour Doppler. J Perinat Med 1999; 27(4):245-9. 43. Goldkrand JW, Hough TM, Lentz SU, et al. Comparison of the amniotic fluid index with gray-scale and colour Doppler ultrasound. J Matern Fetal Neonatal Med 2003 May; 13(5):318-322. 44. Magann EF, Chauhan SP, Barrilleaux PS, et al. Ultrasound estimate of AFV: colour Doppler overdiagnosis of oligohydramnios. Obstet Gynecol 2001 Jul; 98(1):71-4. 45. Magann EF, Chauan Sp, Martin JN Jr. Is AFV status predictive of fetal acidosis at delivery? Aust NZ J Obstet Gynaecol 2003; 43:129-133. 46. Magann EF, Doherty DA, Chauhan SP, Lanneau GS, Morrison JC. Dye-determined AFV and intrapartum/neonatal outcome. J Perinatol 2004; 24:423-428. 47. Rabie N, Magann E, Steelman S, Ounpraseuth S. Oligohydramnios in complicated and uncomplicated pregnancies: a systematic review and meta-analysis.Ultrasound Obstet Gynecol. 2016 Apr 7 48. Magann EF, Chauhan SP, Kinsella MJ, et al. Antenatal testing among 1001 patient at high risk: the role of ultrasonographic estimate of AFV. Am J Obstet Gynecol 1999; 180:1330-1336. 49. Alfirevic Z, Luckas M, Walkinshaw SA, et al. A randomized comparison between amniotic fluid index and maximum pool depth in monitoring of post-term pregnancy. Br J Obstet Gynaecol 1997; 104:207-211. 50. Magann EF, Doherty DA, Field K, et al. Biophysical profile with AFV assessments. Obstet Gynecol 2004; 104:5-10. 51. Moses J, Doherty DA, Magann EF, et al. A randomized clinical trial of the intrapartum assessment of AFV: Amniotic fluid index versus the SDP technique. Am J Obstet Gynecol 2004; 190:1564-1570. 52. Chauhan SP, Doherty DA, Magann EF, et al. Amniotic fluid index vs SDP technique during modified biophysical profile: A randomized clinical trial. Am J Obstet Gynecol 2004; 191:661-668. 53. Sandlin AT, Chauhan SP, Magann EF. Clinical relevance of sonographically estimated AFV: polyhydramnios. J Ultrasound Med 2013; 32(5):851-863. 54. Magann EF, Doherty DA, Chauhan SP, et al. How well do the amniotic fluid index and SDP indices (below the 3rd and 5th and above the 95th and 97th percentiles) predict oligohydramnios and hydramnios? Am J Obstet Gynecol 2004; 190:164-169. 55. Magann EF, Chauhan SP, Doherty DA, et al. A review of idiopathic hydramnios and pregnancy outcomes. Obstet Gynecol Surv 2007; 62:795-802.
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56. Taskin S, Pabuccu EG, Kanmaz AG, Kurtay G. Perinatal outcomes of idiopathic polyhydramnios. Interv Med Appl Sci 2013; 5:21-25. 57. Lallar M, Anam UI Hag, Nandal R. Perinatal outcome in idiopathic polyhydramnios. J Obstet Gynaecol India 2015; 65:310-314. 58. Yefet E, Daniel-Spiegel E. Outcomes from polyhydramnios with normal ultrasound. Pediatrics 2016; 137(2):peds.2015-1948. 59. Golan A, Wolman I, Sagi J, et al. Persistence of polyhydramnios during pregnancy—its significance and correlation with maternal and fetal complications. Gynecol Ovstet Invest 1994; 37(1):18-20. 60. Chauhan SP, Washburne JF, Magann EF, et al. A randomized study to assess the efficacy of the amniotic fluid index as a fetal admission test. Obstet Gynecol 1995: 86(1):9-13.
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Figure 1: Studies that have defined Normal AFV across Gestation Figure 2: AFV assessment with and without Colour Doppler Table 1: Antenatal surveillance tests and their false negative rate
False Negative Rate .4/1000 .6//1000 .8/1000 1.9-5/1000
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Test Contraction Stress Test Biophysical Profile CTG and AFV Estimate CTG only
Table 2: Table of Studies Correlating AFI and SDP
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Measurement Sensitivity to detect AFI/SDP oligohydramnios Magann 33 AFI 6.7% Magann 34 AFI 8.7% Horsager 35 AFI 18% Magann 36 SDP 14% Magann 37 AFI / SDP 10% / 5% AFI = Amniotic Fluid Index; SDP = Single Deepest Pocket
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Study
2000
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Brace & Wolf
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Magann
max at week 34
Queenan
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Amniotic Fluid Volume (mL)
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1000
Sandlin
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max at week 38
max at week 33
100
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EP
max at week 40
16
18
20
22
24
26
28
30
Gestational Age (wks)
32
34
36
38
40
42
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EP
TE D
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SC
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Amniotic fluid volume is critical in the assessment of high risk pregnancies
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Ultrasound estimates of amniotic fluid volume accurately predict normal fluid volumes but inadequately predict abnormal amniotic fluid volumes (oligohydramnios and polyhydramnios) Amniotic fluid Index over diagnoses oligohydramnios leading to more labor inductions without
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improving perinatal outcome
Colour Doppler does not improve the accuracy of identifying actual oligohydramnios
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Single deepest pocket is a better measurement than the amniotic fluid Index in diagnosing
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EP
TE D
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oligohydramnios