Ultrasonography in pregnancy

Int J Gynecol Obstet, 1994, 44: 173-183

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International Federation of Gynecology and Obstetrics

Ultrasonography

in pregnancy

ACOG Technical Bulletin Number 187 (Replaces No. 116, May 1988) Diagnostic ultrasonography is widely used in the assessment of pregnancy and the fetus. Although clinical benefits of routine ultrasonography during pregnancy have not been established, approximately 70% of pregnancies in the United States undergo ultrasound evaluation (1).

Instrumentation Ultrasound is defined as high-frequency sound waves, exceeding 20,000 cycles per second. Frequency refers to the number of peaks or waves that traverse a given point per unit of time and is expressed as hertz (Hz). Instruments used in diagnostic ultrasonography operate at frequencies of 2 million-10 million Hz or 2-10 megahertz (MHz). The higher the frequency of the sound, the shallower the depth of penetration, but the better the resolution of the image produced. Most abdominal ultrasound transducers operate at 3.5-5 MHz, while most vaginal transducers operate at 5-7.5 MHz. Technologic advances in instrumentation have led to significant improvements in image production and resolution. Dynamic, or real-time, ultrasonography creates new images faster than the flicker fusion rate of the eye so that the fetus, or target, appears to be moving in real time. Linear array real-time transducers use a longitudinal series of transducer crystals arranged in sequence to operate serially quite rapidly. Annular array scanners operate similarly but with the serial transducers arranged in concentric rings. Sector realtime ultrasonography uses a single transducer which moves through a prescribed arc. Curvilinear transducers have been introduced recently to incorporate principles of both linear array and sector transducers. Real-time ultrasonography readily detects fetal body motion, cardiac activity, and breathing movements. This dynamic two-dimensional imaging allows evaluation of both structural and functional characteristics of the fetus.

December 1993

Safety Ultrasound energy delivered to a target, such as the fetus, varies with the ultrasound frequency, intensity (power), duration of exposure, and distance from the transducer. A safe level of ultrasound exposure to tissue has been defined arbitrarily as less than 100 mW/cm2 (2). Mostinstrumentsusedindiagnosticultrasonography produce energies no greater than lo-20 mW/cm’ at the transducer face. Ultrasound exposure at intensities usually produced by diagnostic ultrasound instruments has not been found to cause any harmful biologic effects on instrument operators, pregnant women, fetuses, or other patients. Infants exposed in utero have shown no significant differences in birth weight or length, childhood growth, cognitive function, acoustic or visual ability, or rates of neurologic deficits (3,4). Newer applications of ultrasound technology require higher output potentials. Although no adverse fetal effects have been identified to date, increases in the power outputs of ultrasound instruments may increase the potential risks to the fetus. Because of these concerns, many manufacturers include instrumentation on the machines which will continuously display the power output as thermal and mechanical indices. Two principles have been established as guidelines for the ultrasound practitioner. First, the “prudent use” of the equipment is the responsibility of the operator. Second, the operator is responsible for completing the examination using scan modes and power outputs which result in energy exposures which are “as low as reasonably achievable” (5).

Ultrasound Examinations Indications for ultrasonography during pregnancy are multiple and diverse (see the box). The type of examination may vary according to the information sought. Int J Gynecol Obstet 44

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Indications for Ultrasonography During Pregnancy Estimation of gestational age for patients with uncertain clinical dates, or verification of dates for patients who are to undergo scheduled elective repeat cesarean delivery, indicated induction of labor, or other elective termination of pregnancy Evaluation of fetal growth Vaginal bleeding of undetermined etiology in pregnancy Determination of fetal presentation Suspected multiple gestation Adjunct to amniocentesis Significant uterine size/clinical dates discrepancy Pelvic mass Suspected hydatidiform mole Adjunct to cervical cerclage placement Suspected ectopic pregnancy Adjunct to special procedures Suspected fetal death Suspected uterine abnormality Intrauterine contraceptive device localization Biophysical evaluation for fetal well-being Observation of intrapartum events Suspected polyhydramnios or oligohydramnios Suspected abruptio placentae Adjunct to external version from breech to vertex presentation Estimation of fetal weight and/or presentation in premature rupture of membranes and/or premature labor Abnormal serum alpha-fetoprotein value Follow-up observation of identified fetal anomaly Follow-up evaluation of placental location for identified “placenta previa” History of previous congenital anomaly Serial evaluation of fetal growth in multiple gestation Evaluation of fetal condition in late registrants for prenatal care (Adapted from U.S. Department of Health and Human Services. Diagnostic ultrasound in pregnancy. National Institutes of Health publication no. 84-667. Bethesda, Maryland: National Institutes of Health, 1984)

When indicated, a basic ultrasound examination suffices for most obstetric patients. When technically feasible and within the limits of the gestational age at which it is performed, a basic examination should Int J Gynecol Obstet 44

provide the following

information:

??Fetal number ??Fetal presentation ??Documentation

of fetal life

??Placental location ??Assessment ??Assessment

of amniotic fluid volume of gestational age

??Survey of fetal anatomy for gross malformations ??Evaluation

for maternal pelvic masses

A basic ultrasound examination is primarily a metric examination, Nonetheless, a brief survey of fetal anatomy and maternal pelvic organs should be performed. Some major structural malformations of the fetus may be identified during basic examinations, and some basic examinations may suggest the need for a more comprehensive survey. In certain circumstances, a limited ultrasound examination may be appropriate and desirable. Such circumstances commonly relate to the specific nature of the information required or the urgent nature of the clinical situation. A limited examination may be useful to collect information such as the following: ??Assessment

of amniotic fluid volume

??Fetal biophysical

profile testing

??Ultrasonography-guided

amniocentesis

??External cephalic version ??Confirmation ??Localization ??Confirmation

of fetal life or death of placenta in antepartum

hemorrhage

of fetal presentation

A comprehensive ultrasound examination may be indicated for a patient who is suspected of carrying a physiologically or anatomically defective fetus by history, clinical evaluation, or prior ultrasound examination. A limited examination, as defined above, may be performed by ultrasonographers or specially trained personnel. The basic examination, however, should be performed or reviewed by an appropriately trained operator. The comprehensive examination should be performed by an operator with experience and expertise in such scanning. In some situations, it may not be possible to perform a full fetal survey. These include: ??Oligohydramnios ??Hyperflexed

position of the fetus

ACOG Technical Bulletin

??Engagement

of the head

??Compression

of some fetal parts

H Maternal obesity First-Trimester

Pregnancy

Ultrasound scanning in the first trimester may be performed either abdominally or vaginally. The following information should be obtained: ??Presence or absence of an intrauterine ??Identification

gestational

sac

of embryo or fetus

??Fetal number ??Presence or absence of fetal cardiac activity ??Crown-rump length ??Evaluation

of uterus and adnexal structures

Transvaginal scanning with higher-frequency transducers often allows better first-trimester assessment of pregnancy, with earlier detection of fetal echoes and activity. While abdominal scanning reliably detects the gestational sac at 6 weeks of gestation by menstrual dating (6), transvaginal scanning can identify the sac by 5 menstrual weeks of gestation (7, 8). Similarly, fetal echoes should be seen by 7 weeks of gestation via abdominal scanning but prior to 6 weeks of gestation when vaginal scanning is used (7). Generally, fetal heart activity can be detected with abdominal scanning at 7 weeks of gestation by menstrual dating and at 6 weeks of gestation with transvaginal scanning (9). First-trimester bleeding is the most common indication for early ultrasonography. Blighted ovum, or anembryonic pregnancy, can be diagnosed by the failure to detect a fetus within a normal gestational sac after 6 weeks of gestation by menstrual dating. Missed abortion is diagnosed by the absence of cardiac activity in a fetus after 7 weeks of gestation. In patients with suspected ectopic pregnancy, the main contribution of ultrasonography is the demonstration of a gestational sac within the uterus, thereby confirming intrauterine pregnancy. Very rarely, intrauterine and extrauterine (heterotopic) pregnancies may coexist. Although ectopic pregnancy occasionally may be confirmed by demonstration of a gestational sac outside the uterus, both false-positive and false-negative findings hinder the success of ultrasonography alone in diagnosing ectopic gestation. Determining quantitative titers of the beta subunit of human chorionic gonadotropin (B-hCG)

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in serum may help to confirm the diagnosis. Appropriate correlation of ultrasound findings with B-hCG titers requires knowledge of whether the First or Second International Standard is being used (10). Transvaginal scanning may allow earlier detection of the gestational sac than transabdominal scanning. Multiple pregnancy should be diagnosed on firsttrimester ultrasonography only when multiple fetuses, preferably with documented cardiac activity, are demonstrated. Variability in fusion between amnion and chorion in early pregnancy may give the mistaken appearance of more than one gestational sac. Measurement of fetal crown-rump length between 8 and 13 weeks can define gestational age to within 5 days in 95% of cases (11). When measuring the crownrump length, care must be taken to avoid confusing the yolk sac with the fetal head. Second-Trimester

Pregnancy

Obstetric ultrasonography is most often performed to determine gestational age when clinical dating is equivocal or when there is a discrepancy between uterine size and menstrual history. The most commonly used fetal measurements are biparietal diameter, length of the femur or other long bones, and abdominal and head circumferences. Less frequently used parameters are outer orbital diameters, transcerebellar diameter, and length of the foot. It is preferable to use more than one parameter in determining gestational age. The average of the gestational age predictions of biparietal diameter, head circumference, abdominal circumference, and femur length is the best estimate of fetal age (12, 13). This averaging method, however, may be affected adversely by one measurement which is incompatible with other measurements, for example, a small biparietal diameter secondary to compression of the head in oligohydramnios or breech presentation. In such situations, the outlying value can be omitted from the calculation of the mean ultrasound age. Nonetheless, it must be recognized that such outlying values occasionally may indicate an abnormality characterized by an unusual growth pattern of a part, such as a small head or short limbs. When the placental site is being localized in the second trimester, the term “placenta previa” should be used very cautiously because of the potential for relative change secondary to lengthening of the lower uterine segment later in pregnancy. When an abdominal Inr J Gynecol Obsrer 44

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ACOG Technical Bulletin

ultrasound examination is performed at this stage, a distended bladder may give an erroneous impression of placenta previa. This can be resolved by completing the examination after the patient has emptied her bladder. Most placentas that appear to reach the internal OSon second-trimester ultrasonography will not prove to be placenta previa in the third trimester. The appearance of placenta completely covering the internal 0s is an indication for a repeat ultrasound evaluation in the third trimester.

TABLE 1. ASSESSMENTOFGESTATIONALAGE Parameter Crown-rump

length

Biparietal diameter

Gestational Age W)

Range (2SD3 (d)

5-12

*5

12-20

f8

2030

f14

s30 Femur length

f7

20-38

fll

>38

Third-Trimester

Pregnancy

The uniformity of fetal growth that characterizes early

pregnancy is lost later in gestation. Consequently, large variations (f3 weeks) in normal fetal measurements at any given age in the third trimester compromise the accuracy of late pregnancy ultrasonography in establishing gestational age. Nonetheless, measurements in late pregnancy do allow estimation of fetal weight and assessment of fetal growth rate. Estimates of fetal weight are based on regression models which use measurements of two or more gestational age parameters, including head, abdomen, and femur (14). These formulas allow estimation of fetal weight with a 95% confidence interval of S-20%; that is, one standard deviation is generally 7.5-10% of the estimated weight. Unfortunately, fetal weight estimates are much less accurate in predicting the very-low-birth-weight or macrosomic fetus. Fetal growth can be evaluated by measuring growth parameters on serial ultrasound studies. Serial measurements done after 28 weeks of gestation must be spaced at least 2 weeks apart to allow for the inherent error of ultrasound measurements and the decreasing fetal growth rate which occurs normally as gestational age progresses (12, 15). Ultrasound measurements in early pregnancy should be more accurate in determining fetal age and estimating the delivery date than studies done in late pregnancy. When comparing the results of a later study with one done earlier, one must consider the increasing variability (*2 standard deviations) among later gestational age assessments (Table 1). Difficulties encountered particularly in late-third-trimester ultrasonography include a relative paucity of amniotic fluid, the hyperflexed position of the fetus, engagement of the fetal head, and compression of some fetal parts. Methods of evaluating possible intrauterine growth lnt J Gynecol Obstet 44

??

+I21

12-20

f18

SD = standard deviation.

(Adapted from lams JD. Gabbs SG. Intrauterine growth retardation. In: lams JD, Zuspan FP, Quilligan EJ, sds. Manual of obstatrics and gynecology, 2nd ad. St Louis: Mosby, 1990:165-172)

retardation (IUGR) have progressed from biparietal diameter measurement through measurement of abdominal circumference (AC), calculation of the ratios of head circumference (HC) and femur length (FL) to AC, and estimation of fetal weight. When compared with a fetus with normal growth, the AC measurement is relatively small in the fetus with asymmetric IUGR, most likely because of decreased liver glycogen storage. In the normal fetus, the HC/AC ratio falls steadily throughout pregnancy, from a mean of 1.2 at 18 weeks of gestation to 1.0 at 36 weeks. In asymmetric IUGR, the HC remains significantly larger than the AC, and HCYACratios are more than two standard deviations above the expected mean value (16). While the FL/AC ratio in a fetus with normal growth remains approximately 0.22, a ratio greater than 0.24 suggests asymmetric IUGR (17). Assessment of amniotic fluid volume may provide useful information when IUGR is suspected. The value of placental grading is unproven. Fetuses with symmetric IUGR typically have normal HC/AC and FLJAC ratios. Such fetuses comprise approximately 20-25% of cases of IUGR. These cases usually are detected by ultrasonography when all growth parameters lag significantly behind a gestational age confirmed by accurate menstrual history or early ultrasound dating. Vaginal bleeding in the third trimester is an indication for assessing the location of the placenta. Placenta previa may be diagnosed by either transabdominal or transvaginal ultrasonography. With transabdominal scanning, a false-positive diagnosis may occur when

ACOG Technical Bulletin

the bladder is overdistended, as mentioned previously, or when a contraction occurs in the lower segment of the uterus (18). A contraction in the region of the internal OS may bear an ultrasound textural similarity to placental tissue (19). A false-negative diagnosis of placenta previa is very uncommon but may occur when visualization of a posterior placenta previa is prevented by the overlying fetal head or when one fails to scan laterally over the lower uterine segment to identify a lateral placenta previa. In cases of suspected placenta previa, transvaginal scanning may be used to obtain optimal visualization of the placenta and its relationship to the internal OS (20). This procedure is performed when the maternal bladder is empty. The ultrasound transducer should be gently inserted into the vagina, avoiding pressure on the cervix and lower uterine segment.

Surveyof Fetal Anatomy Ultrasound evaluation of fetal anatomy may detect some major structural anomalies. It must be emphasized that it is unrealistic to expect to detect fetal anomalies with 100% accuracy even with the most expert and thorough scanning. A 1989 survey of selected ACOG Fellows revealed that 67% had detected one or more fetal anomalies by ultrasonography, and 51% had missed one or more anomalies (1). Gross malformations such as anencephaly and hydrocephaly were detected most commonly and were seldom overlooked. Anomalies which were more difficult to detect and overlooked more frequently included heart defects, facial clefts, diaphragmatic hernias, skeletal abnormalities, and neural tube defects. Recent studies have shown that transvaginal scanning can detect some anomalies in the first trimester (2 1, 22). Nonetheless, most of these anomalies will be more readily apparent when ultrasound examination is performed later in pregnancy. The basic ultrasound examination should include a survey of fetal anatomy. During the second or third trimester, this examination should include a survey of the following: cerebral ventricles, four-chamber view of the heart (including its position within the thorax), spine, stomach, urinary bladder, umbilical cord insertion site on the anterior abdominal wall, and renal region (9). Where the initial scan shows possible evidence of fetal abnormality, or in cases

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referred because of a specific risk of a fetal abnormality, a more detailed examination will be required. The following guidelines for fetal anatomical survey are designed to aid the practitioner in performing a comprehensive ultrasound examination of the fetus.

Head The fetal head is normally elliptical. In some fetal abnormalities, the cranial configuration may provide valuable diagnostic information. For example, a cloverleaf-shaped cranium may accompany thanatophoric dysplasia or aneuploidy and a lemon-shaped skull may indicate spina bifida. Although the diagnosis of microcephaly can be quite challenging, it must be suspected when fetal head measurements are inappropriately small in relation to other biometric parameters. During a basic ultrasound examination, the appearance of the ventricles shouldbe noted. If they appear to be abnormal, a comprehensive ultrasound examination should be recommended. Hydrocephaly is characterized by enlargement of the ventricular system of the brain, most commonly resulting from obstruction of cerebrospinal fluid circulation. The diagnosis of hydrocephaly may be suspected when any of the following conditions is observed: abnormally increased ratio of lateral ventricular width to hemispheric width, a lateral ventricular atria1 (posterior horn of the lateral ventricle) width greater than 1 cm, a free-floating appearance of the choroid plexus, or asymmetric appearance of the choroid plexus. The ratio of the lateral ventricular width to hemispheric width is normally high during early pregnancy, exceeding 50% from 15-20 weeks of gestation. This ratio decreases with advancing age, falling to 33% by 24 weeks and remaining at this level through delivery. A ratio above 50% after 24 weeks of gestation is considered abnormal (23). The width of the ventricular atrium varies up to 10 mm between 15 and 35 weeks of gestation. Atrial width greater than 10 mm strongly suggests hydrocephaly (24,25). There is frequent association of hydrocephaly with other anomalies, especially spina bifida, and assessment for other anomalies must be completed in making management decisions regarding hydrocephaly. Holoprosencephaly and hydranencephaly also show significant increases of cerebrospinal fluid within the brain. These anomalies generally can be differentiated from hydrocephaly by the absence of midline echoes. Transcerebellar measurements can be studied. ReInt J Gynecol Obstet 44

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cent evidence indicates that in over 90% of cases of open spina bifida, the cerebellar structures are distorted, presumably by downward traction, resulting in an inability to identify the cerebellar bulbs (“banana sign”) or to obtain a transcerebellar measurement that is appropriate for the gestational age (26). The reported incidence of choroid plexus cysts varies from 0.18-3.6% in second-trimester fetuses (2729). Usually located in the posterior aspect of the lateral ventricle, these cysts may be unilateral or bilateral and may vary in size from 2-20 mm. The majority are benign and will resolve by approximately 24 weeks of gestation. Several reports, however, have associated choroid plexus cysts with chromosomal abnormalities (28,30,31). The most commonly noted abnormality is trisomy 18, which occurs in approximately 1% or less of second-trimester fetuses with identified cysts. When choroid plexus cysts are visualized, more extensive scanning should be performed to look for additional abnormalities. Although fetuses with trisomy 18 commonly have multiple anomalies, there are cases in which choroid plexus cysts are the only abnormalities seen (28,30,31). Fetal cystic hygromas are congenital malformations of the lymphatic system which occur most frequently in the nuchal region. On ultrasound examination, a membranelike elevation is seen that is distinct and separate from the skin line of the posterior fetal neck. The area within appears sonolucent and may be septated. Cystic hygromas are commonly associated with hydrops fetalis and chromosomal abnormalities, and additional anomalies have been reported (32). Although monosomy X0 is the most common chromosomal abnormality identified in second- or third-trimester fetuses with cystic hygromas, recent studies in firsttrimester fetuses demonstrate a predominance of fetal aneuploidy (33, 34). Although spontaneous resolution of the hygroma may occur, these fetuses are still at risk for aneuploidy. Fetuses with normal karyotypes and spontaneous resolution of the hygroma have a relatively good prognosis.

echogenic tracts. With these views and a series of transverse scanning ultrasonograms, a spinal defect may be identified if splaying of the lamina or the presence of a sac is detected. Disruption of overlying skin may support the diagnosis. Approximately 10% of neural tube defects are covered by intact skin.

Thorax The fetal lungs are routinely visualized by the middle of the second trimester and normally produce midrange echoes on ultrasound examination. The lungs grow at a rate similar to that of the heart and thorax such that the ratio between cardiac diameter and thoracic circumference remains relatively constant throughout the second and third trimesters (35). A variety of abnormalities may appear as sonolucent, echogenic, or complex areas within the chest, including diaphragmatic hernias, cystic adenomatoid malformations, bronchopulmonary sequestrations, pericardial teratomas, and pleural effusions. A four-chambered view of the fetal heart should be studied. This view is generally obtained by placing the transducer perpendicular to the long axis of the fetal spine. In this view, the heart normally lies in the left anterior quadrant of the chest. The axis of the heart is approximately 45” with a range of 22-75” (36). Deviation of the fetal heart from its normal position is suggestive of an intrathoracic mass or fluid collection. Good visualization of the atria and ventricles, cardiac septa, and outflow tracts should allow detection of 83-92% of structural cardiac anomalies (37, 38). Developmental abnormalities of the fetal diaphragm occur in approximately l/2,000-l/3,000 births. Identification of an apparently intact diaphragmatic outline does not rule out diaphragmatic hernia, especially when a mass or cystic lesion is identified within the fetal chest (39). Prenatal diagnosis of an abnormally small or deformed fetal thoracic cage is most often associated with skeletal dysplasia or prolonged oligohydramnios. An extremely small, bell-shaped chest secondary to either condition correlates highly with lung hypoplasia (40).

Spine

Abdomen

Ultrasound study of the fetal spine is easier in the second trimester than in the third. A sagittal view of the spine should reveal two parallel sets of echoes emanating from the vertebral body and a spinal pedicle. In a coronal view, the pedicles produce a set of parallel

The fetal stomach and urinary bladder usually can be visualized by 14 weeks of gestation. Gastrointestinal obstruction is suspected when one notes an enlarged stomach or dilated loops of bowel or both. Hyperechogenic bowel is a nonspecific finding in a small

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ACOG Technical Bulletin

number of normal fetuses. However, it has been observed with increased frequency in fetuses with Down syndrome (41) or cystic fibrosis (42). Although the cause of this hyperechogenicity is uncertain, in fetuses with cystic fibrosis it most likely represents inspissated meconium. Urinary tract obstruction is suspected when an enlarged fetal bladder or dilated renal pelves are noted. Slight dilatation of the renal pelves is probably physiologic, usually transient, and rarely progressive. The anteroposterior (AP) diameter of the renal pelvis rarely exceeds 10 mm, and the ratio between this pelvic diameter and the AP diameter of the kidney is usually less than 50%. A pelvic diameter greater than 15 mm and a pelviskidney ratio of greater than 50% usually indicates significant hydronephrosis, especially when the renal calyces appear rounded and blunted (43). Fetal kidneys usually can be demonstrated after 16 weeks of gestation. In bilateral renal agenesis, the accompanying oligohydramnios may cause great difficulty in visualizing the fetal abdominal organs and in diagnosing the absence of kidneys. When the kidneys are absent, the adrenal glands enlarge to fill the void and may be mistaken for the kidneys.

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with adverse perinatal outcomes. The increased frequencies of congenital anomalies, growth retardation, and perinatal death require careful evaluation of the fetal status when polyhydramnios or oligohydramnios is present (4547). Although subjective assessment of amniotic fluid volume offers an appropriate screening method, measurement of the amniotic fluid index is a more reproducible and quantitative technique for assessing volume abnormalities (48). The amniotic fluid index represents the sum of the largest vertical pocket of fluid measured in centimeters in each of the four quadrants of the uterus (Fig. 1). These measurements are made with the patient lying supine and the uterus divided into quadrants longitudinally by the midline and transversely midway up the fundus. The scanning transducer is aligned parallel to the midline and perpendicular to the plane of the floor in each quadrant (49). Brief movement of the umbilical cord or a fetal extremity into a fluid pocket does not prevent measurement of the full depth of the pocket. 300 r

Extremities Length of the femur should be measured in the basic examination. If the length of the femur is abnormal, a comprehensive examination should be used to determine the lengths of the other long bones. Various skeletal dysplasias may be suggested by abnormalities in the measurements of the long bones, the shape of these bones, their density, the presence of fractures, or the absence of specific bones. Umbilical

Cord and Abdominal

Wall

When a transverse view of the umbilical cord fails to reveal three vessels, the possibilities of other fetal malformations or karyotypic abnormalities should be considered (44). If only two vessels are seen, a comprehensive ultrasound examination is indicated. Most abdominal wall defects can be excluded by the demonstration of an intact abdomen in the area of umbilical cord insertion.

Fetal Assessment Amniotic

Fluid Index

Abnormalities

of amniotic fluid volume are associated

loo t i 01

15

I

I

I

I

I

I

20

25

30

35

40

45

Gestation (weeks) FIG. 1. Amniotic fluid index (AFI) data from normal patients plotted against gestational week. Upper, middle, and lower lines represent 95th, 50th, and 5th percentile, respectively. (Adapted from Moore TR. Superiority of thefour-quadrantsumoverthesingle-deepest-pocket technique in ultrasonographic identification of abnormal amniotic fluid volumes. Am J Obstet Gynecol 1990;163:762-767) Inr J Gynecol Obstet 44

180

ACOG

Technical

Bulletin

Biophysical Profile Biophysical profile testing consists of a nonstress test with the addition of four observations made by realtime ultrasound. The five components are as follows:

?? Reactive nonstress test ?? Fetal breathing movements (one or more episodes of rhythmic fetal breathing movements of 30 seconds or more within 30 minutes)

?? Fetal movement (three or more discrete body or limb movements

within 30 minutes)

?? Fetal tone (one or more episodes of extension of a

fetal growth retardation, and decreased perinatal mortality rate (5 l-54). Routine ultrasonography in early pregnancy can help to reduce the incidence of labor induction for suspected postdatism and decrease the frequency of undiagnosed major fetal anomalies and undiagnosed twins. However, significant effects on infant outcome are not confirmed by randomized, controlled trials (5 1, 52, 55-60). Although obstetric ultrasound studies are performed routinely in many European countries, in the United States the routine use of ultrasonography cannot be supported from a cost-benefit standpoint.

fetal extremity with return to flexion)

?? Quantitation

of amniotic fluid volume. There is no universal agreement as to the optimal method of assessing amniotic fluid volume. Some investigators consider the detection of a single pocket of amniotic fluid exceeding 2 cm in two perpendicular planes to be adequate. A semi-quantitative, four-quadrant assessment of amniotic fluid depth (amniotic fluid index) is widely used, andcross-sectional nomograms have been developed (48,49). Ideal cutoff levels for intervention using the amniotic fluid index have yet to be established. With this method, a score of 2 (normal) or 0 (abnormal) is assigned to each of the five observations. A score of 8 or 10 is normal; a score of 6 is considered equivocal (a fetus should be retested in 12-24 hours); and a score of 4 or less is abnormal. In the presence of oligohydramnios, further evaluation may be warranted

REFERENCES 1. Horger EO III, Tsai CC. Ultrasound and the prenatal diagnosis of congenital anomalies: a medicolegal perspective. Obstet Gynecol 1989;74:617-619 2. American Institute of Ultrasound in Medicine. Bioeffects considerations for the safety of diagnostic ultrasound. J Ultrasound Med 1988;7(9 Suppl):Sl-S38 3. Stark CR, Orleans M, Haverkamp AD, Murphy J. Shortand long-term risks after exposure to diagnostic ultrasound in utero. Obstet Gynecol 1984;63: 194-200 4. Lyons EA, Dyke C, Toms M, Cheang M. In utero exposure to diagnostic ultrasound: a 6-year follow-up. Radiology 1988;166:687-690 5. American Institute of Ultrasound in Medicine. Bioeffects and safety of diagnostic ultrasound. Rockville, Maryland: AIUM, 1993

(50).

Should All Patients Be Screened? Controversy continues regarding whether ultrasound screening of all obstetric patients improves pregnancy outcome. A consensus development conference convened by the National Institute of Child Health and Human Development in 1984 concluded that no clinical benefit is derived from routine obstetric ultrasonography. However, this workshop did propose 27 indications for ultrasonography during pregnancy (see the box). Commonly advanced arguments in favor of routine scanning include early detection of unsuspected fetal anomalies, early detection of multiple gestation, accurate determination of gestational age leading to improved diagnosis and management of postdatism and Int J Gynecol

Obstet 44

6. Batzer FR, Weiner S, Corson SL, Schlaff S, Otis C. Landmarks during the first forty-two days of gestation by the P-subunit of human chorionic gonadotropin and ultrasound. Am J Obstet Gynecol 1983:146:973-979 7. Fossum GT, Davajan V, Kletzky OA. Early detection of pregnancy with transvaginal ultrasound. Fertil Steril 1988;49:788-791 8. Shapiro BS, Escobar M, Makuch R, Lavy G, DeChemey AH. A model-based prediction for transvaginal ultrasonographic identification of early intrauterine pregnancy. Am J Obstet Gynecol 1992;166:1495-1500 9. American Institute of Ultrasound in Medicine. Guidelines for the performance of the antepartum obstetrical ultrasound examination. Rockville, Maryland: AIUM, 1991 10. American College of Obstetricians and Gynecologists. Ectopic pregnancy. ACOG Technical Bulletin 150. Washington, DC: ACOG, 1990

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11. Robinson HP, Fleming JEE. A critical evaluation of sonar “crown-rump length” measurements. Br J Obstet Gynaecol 1975;82:702-710 12. Hadlock FP, Deter RL, Harrist RB, Park SK. Estimating fetal age: computer-assisted analysis of multiple fetal growth parameters. Radiology 1984;152:497-501 13. Ott WJ. Accurate gestational 1985;66:311-315

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Siedler DE, Filly RA. Relative growth of the higher fetal brain structures. J Ultrasound Med 1987;6:573-576

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Pilu G, Romero R, Reece EA, Goldstein I, Hobbins JC, Bovicelli L. Subnormal cerebellum in fetuses with spina bitida. Am J Obstet Gynecol 1988;158: 1052-1056

27. Clark SL, DeVore GR, Sabey PL. Prenatal diagnosis of cysts of the fetal choroid plexus. Obstet Gynecol 1988;72:585-587

14. Hadlock FP, Harrist RB, Carpenter RJ, Deter RL, Park SK. Sonographic estimation of fetal weight. The value of femur length in addition to head and abdomen measurements. Radiology 1984;150:535-540

28.

Platt LD, Carlson DE, Medearis AL, Walla CA. Fetal choroid plexus cysts in the second trimester of pregnancy: a cause for concern. Am J Obstet Gynecoll991; 164:1652-1656

15. Kurtz AB, Wapner RJ, Kurtz RJ, Dershaw DD, Rubin CS, Cole-Beuglet C, et al. Analysis of biparietal diameter as an accurate indicator of gestational age. J Clin Ultrasound 1980;8:319-326

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Chinn DH, Miller EI, Worthy LM, Towers CV. Sonographically detected fetal choroid plexus cysts: frequency and association with aneuploidy . J Ultrasound Med 1991;10:255-258

16. Campbell S, Thorns A. Ultrasound measurement of the fetal head to abdomen circumference ratio in the assessment of growth retardation. Br J Obstet Gynaecol 1977;84:165-174

30. Achiron R, Barkai G, Katznelson MB-M, Mashiach S. Fetal lateral ventricle choroid plexus cysts: the dilemma of amniocentesis. Obstet Gynecol 199 1;78:8 15-8 18

17. Hadlock FP, Deter RL, Harrist RB, Roecker E, Park SK. A date-independent predictor of intrauterine growth retardation: femur length/abdominal circumference ratio. Am J Roentgen01 1983;141:979-984 18. Townsend RR, Laing FC, Nyberg DA, Jeffrey RB, Wing VW. Technical factors responsible for “placental migration”: sonographic assessment. Radiology 1986; 160: 105-108

31. Perpignano MC, Cohen HL, Klein VR, Mandel FS, Streltzoff J, Chervenak FA, Goldman MA. Fetal choroid plexus cysts: beware the smaller cyst. Radiology 1992;182:715-717 32. Chervenak FA, Isaacson G, Blakemore KJ, Breg WR, Hobbins JC, Berkowitz RL, et al. Fetal cystic hygroma: cause and natural history. N Engl J Med 1983;309:822825

19. Artis AA III, Bowie JD, Rosenberg ER, Rauch RF. The fallacy of placental migration: effect of sonographic techniques. Am J Roentgen01 1985;144:79-81

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20. Brown JE, Thieme GA, Shah DM, Fleischer AC, Boehm FH. Transabdominal and transvaginal endosonography: evaluation of the cervix and lower uterine segment in pregnancy. Am J Obstet Gynecol 1986;155:721-726

34. Shulman LP, Emerson DS, Felker RE, Phillips OP, Simpson JL, Elias S. High frequency of cytogenetic abnormalities in fetuses with cystic hygroma diagnosed in the first trimester. Obstet Gynecol 1992;80:80-82

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36. Comstock CH. Normal fetal heart axis and position. Obstet Gynecol 1987;70:255-259

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This Technical Bulletin was developed under the direction of the Committee on Technical Bulletins of the American College of Obstetricians and Gynecologists as an educational aid to obstetricians and gynecologists. The committee wishes to thank Edgar 0. Horger III, MD, for his assistance in the development of this bulletin. This Technical Bulletin does not define a standard of care, nor is it intended to dictate an exclusive course of management. It presents recognized methods and techniques of clinical practice for consideration by obstetrician-gynecologists for incorporation into their practices. Variations of practice taking into account the needs of the individual patient, resources, and limitations unique to the institution or type of practice may be appropriate.

Copyright 0 December

1993

THE AMERICAN CWEGE OF OBSTETRICIANS AND GYNECOLO6lSTS 488 12th Street, SW Washington, DC #1024-2l88 Int J Gynecol Obstet 44