- Email: [email protected]
Examining Maternal Hydration and Amniotic Fluid Volume
CASE ST u DY
Rebecca is a 33-vear-old gravida 3, para 1011, health care professional a t 31.5 weeks’ gestation currently being treated with 2.5 mg terbutaline and being checked every 4 hours for signs of preterm labor. She has had a n upper respiratory infection with severe nasal congestion for which she had taken Chlor-trimetron ( 4 mg) twice overnight. A nonstress test ( N S T ) was nonreactive. Fetal heart rate baseline was 150 heats/minute, with a n average LTV a n d n o decelerations. O n e contraction was noted in 40 minutes. Biophysical profile score w a s 6/10 (-2 NST, -2 amniotic fluid volume [ A F V ] ) ,with n o cord-free pocket of >2 x 2 cm in t w o dimensions. Amniotic fluid index (AFI) was 2.4 cm. Placenta was posterior and fundal (grade 1). A sonogram 1 week earlier showed fetal growth in the 50th percentile and an AFI of 14.6 cm. After discussion with maternal-fetal medicine personnel, w h o suggested a possible need for delivery because of severe oligohydramnios, the AFI w a s
Studies support the notion that maternal fluid volume may play an important role in maintaining AFV. Sherer et al. ( 1990) reported a case o f severe oligohydramnios in a woman who presented with severe dehydration because of gastroenteritis. After the patient was hydrated with 6,500 ml intravenous crystalloid fluid and was n o longer hypovolemic, a rapid reaccumulation of AFV to normal status was observed. Also, Kilpatrick and Safford (1993) found that fluid restriction decreased the AFI by 8 percent. Kilpatrick and Safford also showed that maternal oral hydration with 2 liters of water over a 2-hour period increased the AFI in pregnancies with normal AFV by 16 percent. Previously, Kilpatrick et al. (1991) had shown that maternal oral hydration with 2 liters of fluids over 2 hours increased the A H by 3 1 percent in women with decreased AFV. In contrast, Flack et al. ( 1 9 9 5 ) a n d Kerr ( I 9 9 6 ) found that oral hydration increased the AFI in w o m e n with oligohydramnios, but did not significantly
Examining Maternal Hydration and Amniotic Fluid Volume Simone Calhoun, RNC, BSN reevaluated a n d 6 hours later w a s found to be 7.8 cm. T h e patient stated t h a t she had been drinking copious a m o u n t s of fluid since the initial AFI. T h e patient continued pregnancy with a twice-weekly N S T a n d amniotic fluid evaluation. T h e AFI remained in the 8to 9-cm range. Terbutaline was discontinued a t 37 wecks. T h e patient spontaneously delivered a 6 pound, 9-ounce healthy boy with Apgar scores of 8 a n d 9 a t 37 weeks, 3 days. M o t h e r a n d infant were discharged after 4 8 hours.
Factors Affecting Amniotic Fluid Volume Historically, oligohydramnios in the absence of rupture of membranes has been considered to be a sign of chronic suboptimal placental function that leads to decreased fetal urine output. Acute decreases in AFV because of inadequate maternal hydration o r medication effects aren’t widely reported. This begs t w o questions: Assuming no technical errors, was the rapidly improved amniotic fluid observed in this case patient due to the effect of oral hydration? Could lack of maternal hydration adversely affect AFV?
December 1999/January 2000
increase AFI in w o m e n with normal a m o u n t s of amniotic fluid. H a c k et al. (199.5) found t h a t the increased AFI w a s not attributable t o increased fetal urine production hut instead w a s probably attributable to improved uteroplacental perfusion caused by maternal plasma volume expansion. Flack e t al.’s research also suggests t h a t there may be fluid passage from t h e maternal intravascular c o m p a r t m e n t into t h e amniotic fluid compartment. Although demonstrated in animal studies, this hasn’t been evaluated i n humans. Animal studies have found significant flows of amniotic fluid through t h e t r a n s m e m b r a n o u s pathway between the fetal vessels o n t h e chorionic plate a n d the amniotic cavity (Flack e t al., 1 9 9 5 ) . Flack e t al. also suggested t h a t AFV volume may be increased by intramembranous net w a t e r transfer between mother a n d fetus across t h e chorionic plate, fetal skin, a n d the surface of the umbilical cord. Kilpatrick a n d Safford ( 1 9 9 3 ) noted a significant increase in umbilical artery mean velocity after maternal hydration a n d theorized t h a t hydration may w o r k to increase t h e AFI by improving placental blood flow or by bulk transfer o f water across t h e placenta.
AWHONN Lifelines
21
Evaluating AFI Normal:
8 ~ 0 1 8 ~
Borderline:
5.1 TO 8.0 CM
Oligohydramnios:
5 cm or less
Conditions Associated with Oligoh~d~amnios Oligohydramnios, when identified in patients with intact membranes in a singleton pregnancy, is defined in several ways in the literature: AFI of less than 5 cm AFI below the fifth percentile for gestational age (normograms have been established for gestational ages) No cord-free fluid pocket that measures > 2 cm in two diameters N o cord-free fluid pocket with at least one 1 cm deep vertical pocket (Moore, 1997) Oligohydramnios complicates approximately 3 to 5 percent of all pregnancies (Flack et al., 199.5). Intrauterine growth restriction, postmaturity syndrome, fetal anomalies, stillbirth, fetal distress in labor, and operative delivery are all associated with oligohydramnios (Kilpatrick, 1997). Prolonged oligohydramnios restricts fetal movement, which may also lead to compression orthopedic abnormalities, and also may interfere with normal fetal lung development leading to lifethreatening compromise caused by to pulmonary hypoplasia (Nimrod et al., 1984). Another concern with inadequate AFV is risk for umbilical cord compression, which may lead to inadequate umbilical circulation. Decreasing AFV in the absence of congenital anomalies is generally thought to be the result of chronically impaired placental function leading to decreased renal blood flow, which decreases fetal urine production (Flack et al., 199.5). Often when the fluid falls below a certain critical point, delivery is recommended (Phelan et al., 1987). If the patient is a t or near term, this is not a difficult medical decision. However, when oligohydramnios is identified in the preterm patient, a decision must be made as to the safety of continuing the pregnancy. In the meanwhile, modified bed rest in lateral recumbent position is often recommended. Prenatal diagnosis should be offered to the family t o rule out aneuploidy (having a n abnormal number of chromosomes). A targeted sonogram should be done to screen for anomalies. The use of corticosteroids if the gestation has been less than 3 4 weeks also is recommended because of the risk for preterm delivery. Women with an AFI below the 5th percentile should be followed-up with a twice-weekly NST and AFI to ensure continued fetal well-being (Moore, 1997). Simone Calhoun, R N C , B S N , I S a perinatal nurse clinician, at St. Francis Hospital and Medical Center in Manchester, C T
22
AWHONN Lifelines
Mechanics of Amniotic Fluid Balance Although the mechanics of amniotic fluid production are not completely understood, it is known that, in most cases, the AFV is maintained by a balance between pro~duction and absorption. Fetal urine is thought to be the major source of amniotic fluid once the fetal kidney begins production at 1 0 to 12 weeks (Moore, 1997). Moore reports on studies showing that at term the human fetus may produce as much as 1,200 ml of urine daily. Another source of amniotic fluid is fetal lung fluid, as evidenced by the presence of pulmonary surfactant in amniotic fluid. Also, it may be movement of amniotic fluid through transmembranous and intramembranous routes, which have been well documented in animal studies (Moore, 1995). Reduction of amniotic fluid from the amniotic cavity is primarily accomplished by fetal swallowing, at a rate of approximately 500 ml/day. Because this process accounts only for about 50 percent of the fluid produced, other mechanisms must be operative. It’s thought that amniotic fluid also may be removed by a transmembranous movement of fluid across the membranes into the maternal circulation (Moore, 1997). It is also possible that amniotic fluid is removed through an intramembranous route into the fetal circulation by way of the blood vessels on the fetal placental surface (Moore, 1997).
€yaluating Amniotic Fluid Volume Because of the increased incidence of poor fetal outcomes associated with oligohydramnios, evaluating AFV has become a n important component of antepartal fetal testing. Several sonographic techniques are used to d o so. Amniotic fluid index appears to be the most widely used technique because of its reproducibility, which allows for comparison among different examiners. This technique divides the uterus into four quadrants, and in each quadrant measures the largest vertical pocket free of umbilical cord or fetal small parts. These dimensions are then totaled to calculate the AFI. Normal AFI ranges between 8 and 1 8 cm (Moore, 1997). An AFI of 5.1 to 8.0 cm is considered to be borderline, and less than 5 cm is defined as oligohydramnios (Kilpatrick et al., 1991; Moore, 1997). Normograms have been developed that establish the expected AFI ranges for each gestational week, because AFI fluctuates throughout gestation. Magann et al. (1997) reported that AFI increased until term, but most research supports that AFV rises progressively throughout pregnancy until about 32 weeks (Flack et al., 1995; Moore, 1997). From 32 weeks until term, AFV is relatively stable, usually at about 700 to 800 ml. Post-term AFV decreases a t about 8 to 1 2 percent per week to about 400 ml at 4 2 weeks (Moore, 1997). The maximum vertical pocket technique (MVP) measures the largest fluid pocket that is free of umbilical cord o r fetal small parts. The use of the MVP technique defines oligohydramnios as the absence of any fluid pocket of at least 1 cm in depth (Moore, 1997). A criticism of this technique is that this criterion was developed from high-risk patients and may not apply to healthy populations (Moore, 1997). Because of this, the MVP technique isn’t widely used today. Another similar Volume 3, lssue 6
FOCUS ON FLUIDS Are you getting enough for You, and Baby, Too? 8 to 12-That’s how many cups of Fluid you need every day if you’re pregnant or breast-feeding.Here’s a guide to help you make sure you get them. Great!
Essential.Good Job Better yet (at least 8 cups) (9 ?o1 1 cups)
MY Daily Fluid Tracker
(1 2 cups)
Total
12
Total
MONDAY
TUESDAY
WEDNESDAY
THURSDAY
FRIDAY
SATURDAY
SUNDAY 1
2
3
4
5
technique in use is the two-diameter pocket, which measures the largest vertical and horizontal pockets. The two-diameter technique defines oligohydramnios as no cord-free pocket measuring greater than 2 x 2 cm (Magann et al., 1992). Another method is the subjective assessment of AFV by the ultrasonographer. This is done by comparing the relative amount of echo-free fluid with the space taken up by the fetus and the placenta. When performed by expert sonographers, this technique can identify oligohydramnios as efficiently as the MVP technique (Moore, 1997). However, this technique is rarely used today, because of the lack of objective measurement, which makes it difficult to follow trends.
Nursing Implications Nurses are in an excellent position to educate women about the importance of adequate daily fluid intake, which, among other benefits, seems to be important in the maintenance of adequate AFV. This may be critical in: The latter stages of pregnancy, when amniotic fluid amounts normally decline In patients at increased risk for oligohydramnios
No published studies determine the actual amount of daily fluid intake needed in pregnancy. Suggested fluid amounts are based on anecdotal information only. Kitzinger (1996) recommends 4 to 5 glasses of water per day, whereas Cherry (1992) recommends that sedentary pregnant women should increase fluids to satisfy December 1999/January 2000
6
7
a
9
10
11
thirst. Cherry also states that active pregnant women need 8 to 12 extra glasses of water per day during exercise. Eagle Family Foods Corp. has a patient teaching tool, Focus on Fluids, that recommends 8 to 12 glasses of fluid daily. All women should be made aware of the importance of adequate fluid intake during pregnancy, not just women at risk for uteroplacental insufficiency. However, it would be of even more importance for women with pregnancies at risk, because inadequate fluid intake may cause further fetal compromise. Studies also point to the importance of maintaining adequate hydration during exercise, thermal exposure, or gastrointestinal losses in pregnancy. The use of antihistamines as described in the case report have played a role in the decreased amniotic fluid. Women should be urged to increase their fluid intake if using these types of over-the-counter medications. In educating clients regarding adequate oral fluids intake, it i s very important to explain the function of amniotic fluid in protecting the fetus from injury and preventing cord compression. Without this information, some women may limit their fluid intake because of increasing edema o r the inconvenience of increased urination late in pregnancy. A fluid tracking chart is available that can be distributed to patients (see “Focus on FI u ids ” ) . In addition to adequate fluid intake, patients with oligohydramnios and intrauterine fetal growth retardation should be encouraged to rest as much as possible in the lateral recumbent position, because this should AWHONN Lifelines
23
optimize uteroplacental perfusion, which also may help to increase AFV as well as optimize fetal growth. Beginning at the 28th week, all gestating women should be instructed to report decreased fetal movement. Some institutions use a modification of the Piacquadio protocol, which quantifies fetal movement in low-risk patients ( M o o r e & Piacquadio, 1989). Patients are given instructions to observe fetal movement 1 hour per day. If the baby moves fewer than 10 times in that hour, they are to eat something nutritious and repeat the observation. If the baby doesn’t move 10 times during the second hour, they are instructed to notify their health care provider immediately. It is important to explain that this does not mean that something is wrong with the baby, but simply that they will need to have fetal evaluation, which should include an AFI to rule out oligohydramnios, which can restrict fetal movement. Because of the many unanswered questions about AFV, more studies are needed to determine adequate fluid intake during pregnancy as well as the degree of fluid restriction that results in oligohydramnios. 4
References Cherry, S . H. (1992). Understanding pregnancy and childbirth (3rd ed.). New York: Collier Books: Macmillan Publishing Co. Flack, N., Sepulveda, W., Bower, S., & Fisk, N., (1995). Acute maternal hydration in third trimester oligohydramnios: effects on uteroplacental perfusion, and fetal urine output. American Journal of Obstetrics and Gynecology, 173(4), 1186-1191. Focus on fluids. (1999). Patient Education Pamphlet. Columbus, Ohio: Eagle Family Foods. Kerr, J., et al. (1996). Maternal hydration and its effect on the amniotic fluid status. (Abstract No. 85). American Journal of Obstetrics and Gynecology, 174( I ) , 416. Kilpatrick, S. 1. (1997). Therapeutic interventions for oligohy-
dydramnios: Amnioinfusion and maternal hydration. Clinical Obstetrics and Gynecology, 40(2),328-336. Kilpatrick, S. J., Safford, K. L., Ponieroy, T., Hoedt, L., Scheerer, I.., Laros, R. K. (1991). Maternal hydration increases amniotic fluid index. Obstetrics and Gynecology, 7 8 ( 6 ) ,1098-1102. Kilpatrick, S. J., & Safford, K. L. (1993). Maternal hydration increases amniotic fluid index in women with normal amniotic fluid. Obstetrics Gynecology, S I ( 1 ), 49-52. Kitzinger, S., ( 1996). The Complete Book of Pregnancy and Childbirth. New York: Alfred A. Knopf, 99. Magann, E. F., Nolan, T. E., Hess, L. W., Martin, R. W., Whitworth, N. S., Morrison, J. C. (1992). Measurement of amniotic fluid: accuracy of ultrasound techniques. American Journal of Obstetrics and Gynecology, 167, 1533-1537. Magann, E. F., Bass, J. D., Chauhan, S. P., Young, R. A., Whitworth, N. S., Morrison, J. C. (1997). Amnioric fluid volume in normal singleton pregnancies. Ohstetrirs C+ Gynecology 90(4), 524-528. Moore, T. R. (1997). Clinical assessment of amniotic fluid. Clinical Obstetrics C+ Gynecology, 40(2),30.3-3 13. Moore, T. R. (1995). Assessment of amniotic fluid in at-risk pregnancies. Clinical Ohstetrics and Gynecology, 3 S ( 1 ), 78-90. Moore, T. R., Piacquadio, K. (1989). A prospective evaluation of fetal movement screening to reduce the incidence of fetal death. American journal Obstetrics & Gynecology, 160, 107.5-1 080. Nimrod, C., Varela-Gettings, F,, Machin G., Campbell, D., 81 Wesenberg, R. (1984). The effect of very prolonged rupture of membranes on fetal development. American Journal of Obstetrics and Gynecology, 148, 40-43. Phelan, J. P., Ahn, M. O., & Smith, C. V. (1987). Amniotic fluid index measurements during pregnancy. ]oumal of Reproductive Medicine 32, 601-604. Sherer, D. M. ( 1 990.) Transient oligohydramnios in a severely hypovolemic gravid women 35 weeks gestation with fluid reaccumulating immediately after intravenous maternal hydration. American Journal Obstetrics and Gynecology, l h 2 ( 3 ) ,770-771.
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AWHONN Lifelines
ssc’,i,j!~,
Volume 3, Issue 6
Rebecca is a 33-vear-old gravida 3, para 1011, health care professional a t 31.5 weeks’ gestation currently being treated with 2.5 mg terbutaline and being checked every 4 hours for signs of preterm labor. She has had a n upper respiratory infection with severe nasal congestion for which she had taken Chlor-trimetron ( 4 mg) twice overnight. A nonstress test ( N S T ) was nonreactive. Fetal heart rate baseline was 150 heats/minute, with a n average LTV a n d n o decelerations. O n e contraction was noted in 40 minutes. Biophysical profile score w a s 6/10 (-2 NST, -2 amniotic fluid volume [ A F V ] ) ,with n o cord-free pocket of >2 x 2 cm in t w o dimensions. Amniotic fluid index (AFI) was 2.4 cm. Placenta was posterior and fundal (grade 1). A sonogram 1 week earlier showed fetal growth in the 50th percentile and an AFI of 14.6 cm. After discussion with maternal-fetal medicine personnel, w h o suggested a possible need for delivery because of severe oligohydramnios, the AFI w a s
Studies support the notion that maternal fluid volume may play an important role in maintaining AFV. Sherer et al. ( 1990) reported a case o f severe oligohydramnios in a woman who presented with severe dehydration because of gastroenteritis. After the patient was hydrated with 6,500 ml intravenous crystalloid fluid and was n o longer hypovolemic, a rapid reaccumulation of AFV to normal status was observed. Also, Kilpatrick and Safford (1993) found that fluid restriction decreased the AFI by 8 percent. Kilpatrick and Safford also showed that maternal oral hydration with 2 liters of water over a 2-hour period increased the AFI in pregnancies with normal AFV by 16 percent. Previously, Kilpatrick et al. (1991) had shown that maternal oral hydration with 2 liters of fluids over 2 hours increased the A H by 3 1 percent in women with decreased AFV. In contrast, Flack et al. ( 1 9 9 5 ) a n d Kerr ( I 9 9 6 ) found that oral hydration increased the AFI in w o m e n with oligohydramnios, but did not significantly
Examining Maternal Hydration and Amniotic Fluid Volume Simone Calhoun, RNC, BSN reevaluated a n d 6 hours later w a s found to be 7.8 cm. T h e patient stated t h a t she had been drinking copious a m o u n t s of fluid since the initial AFI. T h e patient continued pregnancy with a twice-weekly N S T a n d amniotic fluid evaluation. T h e AFI remained in the 8to 9-cm range. Terbutaline was discontinued a t 37 wecks. T h e patient spontaneously delivered a 6 pound, 9-ounce healthy boy with Apgar scores of 8 a n d 9 a t 37 weeks, 3 days. M o t h e r a n d infant were discharged after 4 8 hours.
Factors Affecting Amniotic Fluid Volume Historically, oligohydramnios in the absence of rupture of membranes has been considered to be a sign of chronic suboptimal placental function that leads to decreased fetal urine output. Acute decreases in AFV because of inadequate maternal hydration o r medication effects aren’t widely reported. This begs t w o questions: Assuming no technical errors, was the rapidly improved amniotic fluid observed in this case patient due to the effect of oral hydration? Could lack of maternal hydration adversely affect AFV?
December 1999/January 2000
increase AFI in w o m e n with normal a m o u n t s of amniotic fluid. H a c k et al. (199.5) found t h a t the increased AFI w a s not attributable t o increased fetal urine production hut instead w a s probably attributable to improved uteroplacental perfusion caused by maternal plasma volume expansion. Flack e t al.’s research also suggests t h a t there may be fluid passage from t h e maternal intravascular c o m p a r t m e n t into t h e amniotic fluid compartment. Although demonstrated in animal studies, this hasn’t been evaluated i n humans. Animal studies have found significant flows of amniotic fluid through t h e t r a n s m e m b r a n o u s pathway between the fetal vessels o n t h e chorionic plate a n d the amniotic cavity (Flack e t al., 1 9 9 5 ) . Flack e t al. also suggested t h a t AFV volume may be increased by intramembranous net w a t e r transfer between mother a n d fetus across t h e chorionic plate, fetal skin, a n d the surface of the umbilical cord. Kilpatrick a n d Safford ( 1 9 9 3 ) noted a significant increase in umbilical artery mean velocity after maternal hydration a n d theorized t h a t hydration may w o r k to increase t h e AFI by improving placental blood flow or by bulk transfer o f water across t h e placenta.
AWHONN Lifelines
21
Evaluating AFI Normal:
8 ~ 0 1 8 ~
Borderline:
5.1 TO 8.0 CM
Oligohydramnios:
5 cm or less
Conditions Associated with Oligoh~d~amnios Oligohydramnios, when identified in patients with intact membranes in a singleton pregnancy, is defined in several ways in the literature: AFI of less than 5 cm AFI below the fifth percentile for gestational age (normograms have been established for gestational ages) No cord-free fluid pocket that measures > 2 cm in two diameters N o cord-free fluid pocket with at least one 1 cm deep vertical pocket (Moore, 1997) Oligohydramnios complicates approximately 3 to 5 percent of all pregnancies (Flack et al., 199.5). Intrauterine growth restriction, postmaturity syndrome, fetal anomalies, stillbirth, fetal distress in labor, and operative delivery are all associated with oligohydramnios (Kilpatrick, 1997). Prolonged oligohydramnios restricts fetal movement, which may also lead to compression orthopedic abnormalities, and also may interfere with normal fetal lung development leading to lifethreatening compromise caused by to pulmonary hypoplasia (Nimrod et al., 1984). Another concern with inadequate AFV is risk for umbilical cord compression, which may lead to inadequate umbilical circulation. Decreasing AFV in the absence of congenital anomalies is generally thought to be the result of chronically impaired placental function leading to decreased renal blood flow, which decreases fetal urine production (Flack et al., 199.5). Often when the fluid falls below a certain critical point, delivery is recommended (Phelan et al., 1987). If the patient is a t or near term, this is not a difficult medical decision. However, when oligohydramnios is identified in the preterm patient, a decision must be made as to the safety of continuing the pregnancy. In the meanwhile, modified bed rest in lateral recumbent position is often recommended. Prenatal diagnosis should be offered to the family t o rule out aneuploidy (having a n abnormal number of chromosomes). A targeted sonogram should be done to screen for anomalies. The use of corticosteroids if the gestation has been less than 3 4 weeks also is recommended because of the risk for preterm delivery. Women with an AFI below the 5th percentile should be followed-up with a twice-weekly NST and AFI to ensure continued fetal well-being (Moore, 1997). Simone Calhoun, R N C , B S N , I S a perinatal nurse clinician, at St. Francis Hospital and Medical Center in Manchester, C T
22
AWHONN Lifelines
Mechanics of Amniotic Fluid Balance Although the mechanics of amniotic fluid production are not completely understood, it is known that, in most cases, the AFV is maintained by a balance between pro~duction and absorption. Fetal urine is thought to be the major source of amniotic fluid once the fetal kidney begins production at 1 0 to 12 weeks (Moore, 1997). Moore reports on studies showing that at term the human fetus may produce as much as 1,200 ml of urine daily. Another source of amniotic fluid is fetal lung fluid, as evidenced by the presence of pulmonary surfactant in amniotic fluid. Also, it may be movement of amniotic fluid through transmembranous and intramembranous routes, which have been well documented in animal studies (Moore, 1995). Reduction of amniotic fluid from the amniotic cavity is primarily accomplished by fetal swallowing, at a rate of approximately 500 ml/day. Because this process accounts only for about 50 percent of the fluid produced, other mechanisms must be operative. It’s thought that amniotic fluid also may be removed by a transmembranous movement of fluid across the membranes into the maternal circulation (Moore, 1997). It is also possible that amniotic fluid is removed through an intramembranous route into the fetal circulation by way of the blood vessels on the fetal placental surface (Moore, 1997).
€yaluating Amniotic Fluid Volume Because of the increased incidence of poor fetal outcomes associated with oligohydramnios, evaluating AFV has become a n important component of antepartal fetal testing. Several sonographic techniques are used to d o so. Amniotic fluid index appears to be the most widely used technique because of its reproducibility, which allows for comparison among different examiners. This technique divides the uterus into four quadrants, and in each quadrant measures the largest vertical pocket free of umbilical cord or fetal small parts. These dimensions are then totaled to calculate the AFI. Normal AFI ranges between 8 and 1 8 cm (Moore, 1997). An AFI of 5.1 to 8.0 cm is considered to be borderline, and less than 5 cm is defined as oligohydramnios (Kilpatrick et al., 1991; Moore, 1997). Normograms have been developed that establish the expected AFI ranges for each gestational week, because AFI fluctuates throughout gestation. Magann et al. (1997) reported that AFI increased until term, but most research supports that AFV rises progressively throughout pregnancy until about 32 weeks (Flack et al., 1995; Moore, 1997). From 32 weeks until term, AFV is relatively stable, usually at about 700 to 800 ml. Post-term AFV decreases a t about 8 to 1 2 percent per week to about 400 ml at 4 2 weeks (Moore, 1997). The maximum vertical pocket technique (MVP) measures the largest fluid pocket that is free of umbilical cord o r fetal small parts. The use of the MVP technique defines oligohydramnios as the absence of any fluid pocket of at least 1 cm in depth (Moore, 1997). A criticism of this technique is that this criterion was developed from high-risk patients and may not apply to healthy populations (Moore, 1997). Because of this, the MVP technique isn’t widely used today. Another similar Volume 3, lssue 6
FOCUS ON FLUIDS Are you getting enough for You, and Baby, Too? 8 to 12-That’s how many cups of Fluid you need every day if you’re pregnant or breast-feeding.Here’s a guide to help you make sure you get them. Great!
Essential.Good Job Better yet (at least 8 cups) (9 ?o1 1 cups)
MY Daily Fluid Tracker
(1 2 cups)
Total
12
Total
MONDAY
TUESDAY
WEDNESDAY
THURSDAY
FRIDAY
SATURDAY
SUNDAY 1
2
3
4
5
technique in use is the two-diameter pocket, which measures the largest vertical and horizontal pockets. The two-diameter technique defines oligohydramnios as no cord-free pocket measuring greater than 2 x 2 cm (Magann et al., 1992). Another method is the subjective assessment of AFV by the ultrasonographer. This is done by comparing the relative amount of echo-free fluid with the space taken up by the fetus and the placenta. When performed by expert sonographers, this technique can identify oligohydramnios as efficiently as the MVP technique (Moore, 1997). However, this technique is rarely used today, because of the lack of objective measurement, which makes it difficult to follow trends.
Nursing Implications Nurses are in an excellent position to educate women about the importance of adequate daily fluid intake, which, among other benefits, seems to be important in the maintenance of adequate AFV. This may be critical in: The latter stages of pregnancy, when amniotic fluid amounts normally decline In patients at increased risk for oligohydramnios
No published studies determine the actual amount of daily fluid intake needed in pregnancy. Suggested fluid amounts are based on anecdotal information only. Kitzinger (1996) recommends 4 to 5 glasses of water per day, whereas Cherry (1992) recommends that sedentary pregnant women should increase fluids to satisfy December 1999/January 2000
6
7
a
9
10
11
thirst. Cherry also states that active pregnant women need 8 to 12 extra glasses of water per day during exercise. Eagle Family Foods Corp. has a patient teaching tool, Focus on Fluids, that recommends 8 to 12 glasses of fluid daily. All women should be made aware of the importance of adequate fluid intake during pregnancy, not just women at risk for uteroplacental insufficiency. However, it would be of even more importance for women with pregnancies at risk, because inadequate fluid intake may cause further fetal compromise. Studies also point to the importance of maintaining adequate hydration during exercise, thermal exposure, or gastrointestinal losses in pregnancy. The use of antihistamines as described in the case report have played a role in the decreased amniotic fluid. Women should be urged to increase their fluid intake if using these types of over-the-counter medications. In educating clients regarding adequate oral fluids intake, it i s very important to explain the function of amniotic fluid in protecting the fetus from injury and preventing cord compression. Without this information, some women may limit their fluid intake because of increasing edema o r the inconvenience of increased urination late in pregnancy. A fluid tracking chart is available that can be distributed to patients (see “Focus on FI u ids ” ) . In addition to adequate fluid intake, patients with oligohydramnios and intrauterine fetal growth retardation should be encouraged to rest as much as possible in the lateral recumbent position, because this should AWHONN Lifelines
23
optimize uteroplacental perfusion, which also may help to increase AFV as well as optimize fetal growth. Beginning at the 28th week, all gestating women should be instructed to report decreased fetal movement. Some institutions use a modification of the Piacquadio protocol, which quantifies fetal movement in low-risk patients ( M o o r e & Piacquadio, 1989). Patients are given instructions to observe fetal movement 1 hour per day. If the baby moves fewer than 10 times in that hour, they are to eat something nutritious and repeat the observation. If the baby doesn’t move 10 times during the second hour, they are instructed to notify their health care provider immediately. It is important to explain that this does not mean that something is wrong with the baby, but simply that they will need to have fetal evaluation, which should include an AFI to rule out oligohydramnios, which can restrict fetal movement. Because of the many unanswered questions about AFV, more studies are needed to determine adequate fluid intake during pregnancy as well as the degree of fluid restriction that results in oligohydramnios. 4
References Cherry, S . H. (1992). Understanding pregnancy and childbirth (3rd ed.). New York: Collier Books: Macmillan Publishing Co. Flack, N., Sepulveda, W., Bower, S., & Fisk, N., (1995). Acute maternal hydration in third trimester oligohydramnios: effects on uteroplacental perfusion, and fetal urine output. American Journal of Obstetrics and Gynecology, 173(4), 1186-1191. Focus on fluids. (1999). Patient Education Pamphlet. Columbus, Ohio: Eagle Family Foods. Kerr, J., et al. (1996). Maternal hydration and its effect on the amniotic fluid status. (Abstract No. 85). American Journal of Obstetrics and Gynecology, 174( I ) , 416. Kilpatrick, S. 1. (1997). Therapeutic interventions for oligohy-
dydramnios: Amnioinfusion and maternal hydration. Clinical Obstetrics and Gynecology, 40(2),328-336. Kilpatrick, S. J., Safford, K. L., Ponieroy, T., Hoedt, L., Scheerer, I.., Laros, R. K. (1991). Maternal hydration increases amniotic fluid index. Obstetrics and Gynecology, 7 8 ( 6 ) ,1098-1102. Kilpatrick, S. J., & Safford, K. L. (1993). Maternal hydration increases amniotic fluid index in women with normal amniotic fluid. Obstetrics Gynecology, S I ( 1 ), 49-52. Kitzinger, S., ( 1996). The Complete Book of Pregnancy and Childbirth. New York: Alfred A. Knopf, 99. Magann, E. F., Nolan, T. E., Hess, L. W., Martin, R. W., Whitworth, N. S., Morrison, J. C. (1992). Measurement of amniotic fluid: accuracy of ultrasound techniques. American Journal of Obstetrics and Gynecology, 167, 1533-1537. Magann, E. F., Bass, J. D., Chauhan, S. P., Young, R. A., Whitworth, N. S., Morrison, J. C. (1997). Amnioric fluid volume in normal singleton pregnancies. Ohstetrirs C+ Gynecology 90(4), 524-528. Moore, T. R. (1997). Clinical assessment of amniotic fluid. Clinical Obstetrics C+ Gynecology, 40(2),30.3-3 13. Moore, T. R. (1995). Assessment of amniotic fluid in at-risk pregnancies. Clinical Ohstetrics and Gynecology, 3 S ( 1 ), 78-90. Moore, T. R., Piacquadio, K. (1989). A prospective evaluation of fetal movement screening to reduce the incidence of fetal death. American journal Obstetrics & Gynecology, 160, 107.5-1 080. Nimrod, C., Varela-Gettings, F,, Machin G., Campbell, D., 81 Wesenberg, R. (1984). The effect of very prolonged rupture of membranes on fetal development. American Journal of Obstetrics and Gynecology, 148, 40-43. Phelan, J. P., Ahn, M. O., & Smith, C. V. (1987). Amniotic fluid index measurements during pregnancy. ]oumal of Reproductive Medicine 32, 601-604. Sherer, D. M. ( 1 990.) Transient oligohydramnios in a severely hypovolemic gravid women 35 weeks gestation with fluid reaccumulating immediately after intravenous maternal hydration. American Journal Obstetrics and Gynecology, l h 2 ( 3 ) ,770-771.
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Volume 3, Issue 6