Ultrasound evaluation of amniotic fluid volume. II. The relationship of increased amniotic fluid volume to perinatal outcome

Nature and frequency of chromosomal abnormalities in pregnancies with abnormal ultrasound findings: an analysis of 117 cases with review of the literature

During a 7-year period, 117 fetal karyotypes were available from 131 genetic amniocenteses. These procedures were performed between 14 and 37 weeks' gestation for the following abnormal ultrasound findings: (1) intrauterine growth retardation (IUGR)--61 cases; (2) fetal malformation--71 cases; and (3) amniotic fluid volume (AFV) abnormality--60 cases. Chromosomal abnormalities were identified in 19 cases (16.2 per cent). Aneuploidy was 2.5 times as frequent in the presence of malformations than in their absence. No correlation was demonstrated between specific fetal malformations and specific chromosomal abnormalities. Aneuploidy was also twice as frequent in the presence of symmetrical IUGR than in its absence. No chromosomal abnormalities were found among eight cases of asymmetrical IUGR. Four cases of aneuploidy presented with isolated IUGR, three of these involving the X chromosome. The frequency of aneuploidy was the same with or without abnormalities of AFV (14.3 versus 16.4 per cent). No chromosomal abnormality was found associated with isolated AFV abnormalities.

Fetal growth disturbances

IUGR is a fetal disorder characterized by diminished fetal growth, especially in the third trimester. Growth retardation may be due to primary placental insufficiency or may result from a variety of maternal or fetal causes and is associated with elevated perinatal mortality and morbidity. Numerous conventional and Doppler ultrasound criteria have been proposed for diagnosing IUGR prenatally, but none on its own permits confident diagnosis of this condition. Diagnosis or exclusion of IUGR can best be achieved by the combined use of three parameters: estimated fetal weight, amniotic fluid volume, and maternal hypertension. When IUGR is suspected based on these parameters, Doppler ultrasound can help to determine the prognosis. Large fetuses, particularly those weighing more than 4,000 grams at birth, are at risk for perinatal morbidity and mortality due to obstetrical complications. These fetuses occur more frequently and are at especially high risk in diabetic mothers. The estimated fetal weight is the most direct parameter for diagnosing LGA and macrosomia and is moderately accurate with positive predictive values up to 67% in the general population and 77% in diabetics. It can be an important factor in deciding on the route of delivery in diabetic mothers.

Superiority of the four-quadrant sum over the single-deepest-pocket technique in ultrasonographic identification of abnormal amniotic fluid volumes

Ultrasonographic estimation of amniotic fluid volume is an important adjunct to assessment of fetal well-being. However, no single method has emerged as most predictive. Many ultrasonographers use subjective or single-pocket guidelines in evaluation of amniotic fluid volume. We therefore assessed the ability of a maximum-vertical-pocket technique to identify patients with abnormal volumes of amniotic fluid. A total of 1168 patients was studied. Oligohydramnios (n = 76) was defined as an amniotic fluid index less than 5th percentile for gestational age (70 to 98 mm). Hydramnios (n = 51) was defined when the amniotic fluid index was greater than 95th percentile (185 to 249 mm). The ability of the maximum-vertical-pocket technique to identify cases with oligohydramnios by amniotic fluid index was poor: sensitivity was 42% and positive predictive value was 51%. Fifty-eight percent of cases with oligohydramnios by amniotic fluid index had "normal" values according to the single-pocket technique. The correlation coefficient between amniotic fluid index and maximum vertical pocket was 0.51, R2 = 24%. The correlation between the maximum vertical pocket and amniotic fluid index was somewhat better in cases of polyhydramnios (r = 0.79, R2 = 62%), but the sensitivity, positive predictive value, and false-negative rates were high as in oligohydramnios. These data suggest that the maximum-vertical-pocket technique has adequate specificity but is a poor screening tool. The results demonstrate that use of gestation-specific norms for the amniotic fluid index identifies abnormal amniotic fluid volumes more efficiently than the single-pocket technique.

The amniotic fluid index in normal human pregnancy

The four-quadrant sum of amniotic fluid pockets (amniotic fluid index) was studied prospectively in 791 normal pregnancies. Interobserver and intraobserver variation was 3.1% and 6.7%, respectively. Logarithmic transformations were used to establish the mean and 90% confidence intervals for the amniotic fluid index at each week of gestation. In term pregnancies, the boundaries of the amniotic fluid index were 115 mm (mean), 68 to 196 mm (5th to 95th percentiles). In postdates pregnancies greater than 42 weeks, the values were 108 mm (mean), 67 to 174 mm (5th to 95th percentiles), p less than 0.0001. However, the values for each week were statistically distinct, indicating the need to reference amniotic fluid index measurements to week-specific normative tables for accurate interpretation. This study provides normative data for the amniotic fluid index throughout pregnancy.

Maternal indomethacin therapy in the treatment of polyhydramnios

Fifteen patients with polyhydramnios and clinical symptoms related to excess amniotic fluid volume were treated with indomethacin therapy that was started at a mean gestational age of 27.4 +/- 2.79 weeks and discontinued at a mean gestational age of 32.9 +/- 1.83 weeks. Patients were treated with 2.0 to 2.2 mg of indomethacin per kilogram of body weight per day, either orally or by rectal suppositories. No therapy was administered after 35 weeks, and the duration of therapy was no longer than 4 weeks. The majority of fluid reduction occurred within the first week of treatment. Subsequently, a smaller but steady reduction of fluid was observed. All patients were delivered after 38 weeks with a mean birth weight of 3543 +/- 586.3 gm. Examinations of newborns at birth and follow-up at 3 months, 6 months, and 1 year revealed no adverse effects of indomethacin administration.

Early prediction of fetal macrosomia in diabetes mellitus

We studied 374 pregnant diabetic women to determine the value of various ultrasound parameters in the prediction of fetal macrosomia. The correlation between ultrasonographic signs and maternal glycaemia in the development of fetal macrosomia was also studied. Significant correlation was observed between the accurence of hydramnios and future macrosomia during the second-trimester (p less than 0.001). Serum fructosamine levels as an index of maternal glycaemia in patients of macrosomic fetuses were significantly higher throughout the pregnancy as compared with mothers of infants with normal birth weight (p less than 0.001). These data suggest: 1. The presence of hydramnios in the second trimester is a useful predictor of macrosomia in diabetic patients (specificity: 86%, negative predictive value: 88%). 2. Maternal diabetic control during pregnancy has a significant influence on fetal growth and contributes to the development of fetal macrosomia. 3. The lack of correlation between the frequency of hydramnios and fructosamine levels suggests that a mechanism other than carbohydrate metabolism also plays an important role in the development of fetal macrosomia.

Stillbirths: a clinicopathological survey (1972-1982)

A survey of 325 stillbirths from 27,072 babies delivered at University College Hospital Galway from April 1, 1972 to March 31, 1982, gave a stillbirth rate of 12 per thousand, which, when corrected for 66 lethal congenital abnormalities, became 9.6 per thousand. The cause of death in each stillbirth was determined clinically and pathologically where possible and was classified according to a modified Aberdeen classification of perinatal death. Consideration of the birth weights of the babies who died showed that 223 (68.6%) weighed over 1,500 g, and excluding those with abnormalities, they must be considered salvageable with the application of intensive neonatal care. There were 54 (16.6%) intrapartum deaths, which must also be considered preventable. The application of ultrasonic surveillance should complement clinical acumen, by allowing easier detection of the fetus at risk, thereby facilitating earlier intervention which in turn should reduce antenatal stillbirths.

Normal amniotic fluid volume changes throughout pregnancy

The purpose of this study was to provide a quantitative characterization of the changes in amniotic fluid volume that occur throughout gestation. From 705 published amniotic volumes for normal pregnancies, we found that after log transformation, amniotic fluid volume had a uniform variability over 8 to 43 weeks' gestation. Thus the 95% confidence interval covered the range of 1/2.57 to 2.57 times the mean volume at any given gestational age. Contrary to expected trends, mean amniotic fluid volume did not change significantly between 22 and 39 weeks and averaged 777 ml, with the 95% confidence interval ranging from 302 to 1997 ml. The data are summarized in nomograms covering 8 to 43 weeks' gestation.

Chromosomal prenatal diagnosis: study of 936 cases of intrauterine abnormalities after ultrasound assessment

Nine hundred and thirty-six prenatal chromosomal analyses were performed by four cytogenetic centres after ultrasound diagnosis of fetal abnormalities, amniotic fluid disorders, fetal growth retardation, and fetal or placental abnormalities. During the same period, 6515 fetal karyotypes were analysed because of maternal age. Frequencies of chromosomal aberrations in each case were respectively 4.4, 6.7 and 15.8 per cent, compared with 3.18 per cent when the fetal karyotype was performed because of maternal age. High rates of chromosomal aberrations are observed in cases of cervical hygroma, limb abnormalities, omphaloceles, duodenal stenosis, hydrocephalus, and facial abnormalities. In the case of polymalformations, this rate was 29.2 per cent. When malformations were seen together with an amniotic fluid disorder or growth retardation, 21.5 per cent chromosomal aberrations were observed. This frequency was 10.4 per cent when growth retardation was associated with an amniotic fluid disorder. Trisomy 13, 18, 21 and monosomy X accounted for 4/5 of all abnormalities in which we observed a high rate of triploidies (4.9 per cent) and balanced (3.3 per cent) or unbalanced (9.8 per cent) non-Robertsonian structural abnormalities. Sonographic ascertainment of these aberrations and prenatal characteristics of major anomalies are discussed.

Twin with hydramnios: treating premature labor at source

Six twin pregnancies complicated by hydramnios and premature labor were prospectively studied to determine whether indomethacin reduces amniotic fluid. Requirements for study entry included a gestational age less than 32 completed weeks and an amniotic fluid greater than 10 cm in one or both sacs. The amniotic fluid was measured using real-time ultrasonography before, during, and after treatment. Indomethacin treatment was initiated as a 100 mg rectal suppository and maintained thereafter by 50 mg orally every 6 hours. Treatment was discontinued after 32 completed weeks' gestation, if the patient was asymptomatic and the amniotic fluid was "normal" (less than 8 cm) or after the onset of oligohydramnios in one or both sacs (less than 2 cm). The interval from initiation of treatment to delivery ranged from 12 to 101 days. A coincidental reduction in amniotic fluid was observed in all seven treatment cycles. The time interval to obtain "normal" fluid ranged from 4 to 20 days (mean, 12.5 days). There were no perinatal complications attributable to indomethacin treatment. These data suggest that in selected pregnancies complicated by hydramnios, indomethacin may be of value not only in prolonging gestation but also in amniotic fluid reduction.

The relationship of increased amniotic fluid volume to perinatal outcome

We studied a group of 135 patients with polyhydramnios diagnosed on the basis of ultrasonic findings (greatest vertical diameter of the liquor column greater than or equal to 8.0 cm) between 32 and 36 weeks gestation (study group). We compared the obstetric characteristics and perinatal outcome of the study group with a similar number who constituted our control group. The incidence of women aged 20 years or less was higher in the study group (8.9%) compared with 4.5% in the control group. Of the 135 patients who were diagnosed to have polyhydramnios ultrasonically, the clinical diagnoses prior to referral for ultrasonic scanning, were, suspected large for date fetuses in 34 patients (25.2%), clinically suspected polyhydramnios in 28 (20.7%), gestational diabetes in 21 (15.6%) and insulin dependent diabetes in 6 (4.4%) compared with 13.3%, 5.2%, 3.0% and 0.7%, respectively in the control group (P less than 0.05). Preterm delivery occurred in 11.1% in the study group compared with the incidence of 6.7% in the control group. The incidence of fetal distress, low Apgar Score, macrosomic infants, major fetal anomalies, gross and corrected perinatal mortality rate and admission to special/intensive care nursery was significantly higher in the study group compared with that of the control (P less than 0.01). We found ultrasonic examination is a reliable technique to assess the amount of amniotic fluid volume and it alerts the clinician to possible future problems in pregnancy, labor and neonatal period.

The efficacy of starting postterm antenatal testing at 41 weeks as compared with 42 weeks of gestational age

Postterm antenatal fetal surveillance has traditionally begun at 42 completed weeks of gestation. However, recent data have shown that a significant percentage of cases of perinatal asphyxia occurs between 40 and 42 weeks of gestation. We compared the perinatal outcome of fetuses with antenatal surveillance beginning at 41 weeks to those starting at 42 weeks of gestation. The study groups consisted of 908 patients who began antenatal testing at 41 weeks and 352 who began testing at 42 weeks. Antenatal testing consisted of twice-weekly amniotic fluid assessments and nonstress tests (including evaluation for late and variable decelerations). Between 41 and 42 weeks, the group whose testing started at 41 weeks had an overall incidence of intrapartum fetal distress of 2.7%, no stillbirths, and no infants with major neonatal morbidity. Patients without antenatal testing who delivered between 41 to 42 weeks did not have a significantly increased incidence of fetal distress (3.3%; p = 0.07). However, this group had a significantly increased incidence of adverse outcomes (p less than 0.05), including three stillbirths and seven cases of major neonatal morbidity. Beyond 42 weeks, the group whose testing started at 41 weeks had a 2.3% overall incidence of fetal distress. This was significantly less (p less than 0.01) than the group whose testing started at 42 weeks (5.6%). Neither of the groups had any stillbirths or infants with major neonatal morbidity. These findings suggest that starting antenatal testing at 41 weeks of gestation may result in decreased postterm perinatal mortality and morbidity as well as a decreased incidence of intrapartum fetal distress.

Antepartum predictors of fetal distress in postterm pregnancy

The purpose of this study was to determine the efficacy of combining nonstress testing with ultrasound assessment of amniotic fluid volume for the antenatal evaluation of the postterm fetus. Postterm patients (884) were managed with amniotic fluid assessments and nonstress tests (including evaluation for variable and late decelerations) twice a week. There were no perinatal deaths or major neonatal morbidity. However, the antenatal testing sensitivity, specificity, negative, or positive predictive values were not improved by combining the two tests. Individually, amniotic fluid assessment was just as accurate a predictor of fetal well-being and was a significantly more sensitive test than the nonstress test. In addition, antenatal predictors of fetal distress and intrapartum signs of fetal distress were almost exclusively those reflective of umbilical cord compromise. These findings stress the importance of antenatal screening for signs of umbilical cord compromise as an early indication of potential fetal compromise. Although the results also suggest that amniotic fluid assessment is superior to the nonstress test, they do not conclusively support the use of amniotic fluid assessment as the sole parameter for postterm antenatal surveillance.

Treatment of polyhydramnios with prostaglandin synthetase inhibitor (indomethacin)

Polyhydramnios, which is caused by an excess of amniotic fluid, was diagnosed uniformly in eight patients by ultrasound examination and clinical symptoms, namely, premature uterine contraction, abdominal pain, and respiratory discomfort that resulted from excessive pressure on the diaphragm. Fetal anomalies incompatible with extrauterine existence were excluded by serum alpha-fetoprotein levels, repeated sonography, amniocentesis, and chromosomal analyses. Patients were treated with 2.2 to 3.0 mg of indomethacin/kg body weight/day. The treatment was started at an average gestational age of 24 +/- 0.5 weeks and continued for 2 to 11 weeks. All patients had significant improvement with a simultaneous reduction in amniotic fluid volume, fundal height, and umbilical perimeter. All patients were delivered satisfactorily at an average of 39 weeks' gestation. The fetuses were within the normal body weight range of 2750 to 3600 gm and showed normal development during the neonatal period of 2 to 6 months. Before delivery without indomethacin, the polyhydramnios reformed. Adverse effects or intolerance to the drug was avoided by either a reduction in the dose or cessation of indomethacin therapy. Our studies suggest that indomethacin therapy is an effective way to manage pregnancy complicated by polyhydramnios.

Identification of the small for gestational age fetus with the use of gestational age-independent indices of fetal growth

This study reviews the roles of sonographic assessment of the rate of growth of the fetal abdominal circumference, the femur length/abdominal circumference ratio, and qualitative determination of amniotic fluid volume as gestational age-independent indices for identification of the small for gestational age fetus. The sensitivity and specificity for single and combinations of test results were evaluated in 50 appropriate for gestational age and 40 small for gestational age fetuses. Positive and negative predictive values were derived for the general population. Our results indicate that either a rate of growth of the fetal abdominal circumference less than or equal to 10 mm/14 days or a femur length/abdominal circumference ratio greater than or equal to 23.5 correctly identifies most small for gestational age fetuses. When the general population is screened, only 15% of small for gestational age fetuses will be missed by this combination of criteria. The presence of a pocket of amniotic fluid less than or equal to 2.0 cm is highly suggestive of a small for gestational age fetus. However, the presence of a pocket of amniotic fluid greater than 2.0 cm does not guarantee an appropriate for gestational age fetus. We conclude that these gestational age-independent indices of fetal growth offer useful tools for differentiating between the small for gestational age and appropriate for gestational age fetus.

Limitations of using maximum vertical pocket and other sonographic evaluations of amniotic fluid volume to predict fetal growth: technical or physiologic?

Maximum vertical pocket measurement and subjective sonographic impression of amniotic fluid volume were studied in 487 selected pregnancies. Opiate abuse, suspected fetal growth retardation, and suspected postterm gestation were negatively correlated with maximum vertical pocket; suspected fetal growth acceleration and increasing birth weight were positively correlated. Maximum vertical pocket appeared to peak at 31 to 33 weeks (p less than 0.05), and was related to fetal growth (p less than 0.001). Subjective sonographic evaluation of amniotic fluid volume yielded comparable results. Unfortunately, neither technique could be used to accurately predict the birth of a small, appropriate, or large for gestational age infant in the individual pregnancy. Abnormal fetal growth could be reliably excluded in only a small number of cases. This and previous studies suggest that diagnosis of abnormal fetal growth by means of sonographic amniotic fluid volume evaluation could be limited by physiologic variation rather than technical error in measurement.