Longitudinal assessment of amniotic fluid index

A contemporary amniotic fluid volume chart for the United States: The NICHD Fetal Growth Studies-Singletons

BACKGROUND

Amniotic fluid is essential to normal fetal development and is estimated clinically with ultrasound scanning to identify pregnancies that are at risk for poor perinatal outcome.

OBJECTIVE

Our goal was to develop a United States standard for amniotic fluid volume that is estimated by the amniotic fluid index and single deepest pocket.

STUDY DESIGN

We performed a planned secondary analysis of a multicenter observational study of 2334 low-risk women with normal singleton gestations from 1 of 4 self-reported racial/ethnic groups. Eligible women had confirmed first-trimester dating criteria with health status, lifestyles, and medical and obstetric histories that were associated with normal fetal growth. Consenting women underwent serial (up to 5) sonographic evaluations of amniotic fluid between 15 and 40 weeks of gestation after being assigned randomly to 1 of 4 gestational age observation schedules. Twelve United States perinatal centers participated, and all sonograms were performed by credentialed sonographers who used identical, high-resolution equipment; caregivers were unaware of results but were notified for oligohydramnios. Women (n=597) who were subsequently found to have clinically significant antepartum complications were excluded. Racial/ethnic-specific nomograms for amniotic fluid index and single deepest pocket across gestation were developed with the use of linear mixed models with cubic splines; racial/ethnic differences were evaluated both with global and between-group tests. Median, 3rd, 5th, 10th, 90th, 95th and 97th percentile values were also estimated. We further considered the possible confounding effects of selected maternal characteristics and the estimated fetal weight at each sonogram.

RESULTS

A total of 1719 pregnant women met inclusion criteria and had available data. These included 480 non-Hispanic white women, 418 non-Hispanic black women, 485 Hispanic women, and 336 Asian women. Both the amniotic fluid index and the single deepest pocket varied across gestation with maximal values at 26 and 33 weeks of gestation, respectively. Statistically significant differences were observed by maternal race/ethnicity. The between-group differences that were observed at 17-22 and 35-40 weeks of gestation remained statistically significant after adjustment for maternal characteristics and estimated fetal weight. These between-group racial/ethnic differences were most prominent after 35 weeks of gestation and at the extremes of dispersion (3rd and 97th percentiles). All 3rd and 97th percentile amniotic fluid index values were within the range of commonly used cutoffs to define oligohydramnios (≤5 cm) and polyhydramnios (≥25 cm). However, the 3rd percentile values ranged between 5.9 cm at 40 weeks of gestation and 10.1 cm at 25-27 weeks of gestation; the 97th percentile values ranged between 24.8 cm at 38 weeks of gestation and 15.7 cm at 15 weeks of gestation.

CONCLUSION

Sonographic amniotic fluid volume estimates vary by racial/ethnic group, but the absolute differences appear to be small and may not be clinically significant. Selected maternal characteristics and estimated fetal weight did not affect the racial/ethnic differences. Between-group differences are maximal after 35 weeks of gestation and at the extremes of the upper and lower dispersion estimates. Given the observed variability in extreme (3rd and 97th percentile) dispersion values over the gestation, use of single cutoffs to define out-of-range measurements may not be appropriate clinically. These data might form a contemporary United States standard for amniotic fluid estimation that uses the amniotic fluid index and the single deepest pocket.

Association between amniotic fluid evaluation and fetal biometry: a prospective French "Flash" study

We aimed to study the association between three different methods of assessing the amount of amniotic fluid (subjective method (SM), deepest vertical pocket (DVP) and amniotic fluid index (AFI)) and estimated fetal weight (EFW) (in percentile or Z-score) after adjustment on maternal-fetal parameters. We performed a nationwide cross-sectional study through the French network of obstetric sonographers using the "flash" study method and including low-risk singleton pregnancies from 18-40 weeks. Crude and adjusted odds ratio were computed after stratification upon 2nd and 3rd trimester of pregnancy. 1667 ultrasound scans performed by 65 operators were included. Only Z-score of EFW was significantly associated with SM in both trimesters. For DVP and AFI, Z-score of EFW and male fetal gender was significantly associated with them in 2nd trimester. In the 3rd trimester, both Z-score of EFW and large (LGA) or small for gestational age (SGA) fetus were significantly associated with AFI. and DVP. Overweight woman and class I obesity women were also significantly associated with DVP modification. In conclusion, all three methods of amniotic fluid evaluation are significantly associated to estimated fetal weight. DVP and AFI appeared equivalent except that maternal-fetal factors seemed to have a higher impact in DVP than AFI.

Longitudinal assessment of amniotic fluid volume in monoamniotic twin gestations

OBJECTIVE

The aim of this study is to describe normal amniotic fluid volume through gestation in a cohort of normal monoamniotic (MA) twins.

METHOD

Our ultrasound database was queried for MA twin gestations from 2004 to 2011. Monochorionic twin pregnancies mimicking MA gestations, such as twin-twin transfusion syndrome, were excluded. Complicated MA gestations and higher-order multifetal gestations involving an MA pair were excluded. Thirty subjects were followed with serial amniotic fluid index (AFI) measurements from 15 to 32 weeks gestation. Using each AFI measurement as a unique data point, a quadratic regression model and a multi-level growth model were developed against gestational age (GA), providing a predicted AFI at each completed week, with a 95% confidence interval.

RESULTS

The quadratic regression least squares and multi-level growth models yielded the same curve comparing the AFI to the GA. Figure 1 depicts the model with the 95% confidence interval for normal amniotic fluid volume by GA for normal MA twins. Table 2 shows the 5th, 50th, and 95th percentiles for AFI by week from 15 to 32 weeks.

CONCLUSION

We have generated normative data for amniotic fluid volume across gestation in uncomplicated MA twins. This can be used as a reference when managing MA pregnancies.

Management of oligohydramnios in pregnancy

The finding of oligohydramnios in pregnancy is problematic. The various mechanisms that control amniotic fluid, the inability to precisely measure and quantify the amount, and the relevance of a "decreased" amount of fluid make the management of this finding unclear. Given the limited amount of data, the single deepest vertical pocket may be a better method than the amniotic fluid index to define oligohydramnios. A large prospective study is needed to develop the most optimal management recommendations, especially for idiopathic oligohydramnios at or near term.

Biochemical amniotic fluid pattern for prenatal diagnosis of esophageal atresia

Prenatal diagnosis of esophageal atresia (EA) may improve the outcome of affected neonates by allowing optimization of both prenatal and postnatal care. Prenatal sonographic detection is based on polyhydramnios and/or nonvisualization of the fetal stomach bubble, two signs with a large number of etiologies. We evaluated a biochemical approach to improving diagnostic efficiency. We compared amniotic fluid biochemical markers in 44 EA cases with 88 polyhydramnios and 88 nonpolyhydramnios controls. Both matched for GA with cases. Total proteins, alpha-fetoprotein (AFP), and digestive enzyme activities were assayed, including gamma-glutamyl transpeptidase (GGTP). We defined an EA index (AFP multiplied by GGTP). A significant difference (p < 0.0001) was observed for total protein, AFP, GGTP, and EA index between the EA group and each of the two control groups. No statistical difference was observed for any marker between the two most frequent EA subgroups (type I and type III) or between the two control groups. Using a cutoff of 3 for the EA index, 98% sensitivity and 100% specificity were observed for amniotic fluid prenatal diagnosis of EA, whatever the anatomical type. A large prospective series is required to confirm these results.

Fetal urine production in late pregnancy

Objective. Hourly fetal urine production rate (HFUPR) was studied in relation to both gestational age and the onset of spontaneous labor in normal term human pregnancies. Methods. Serial volume measurements were obtained from longitudinal ultrasound images of the fetal bladder at 1-5-minute intervals, and HFUPR was subsequently calculated. A total of 178 adequate bladder-filling cycles were recorded in 112 women, and the amniotic fluid index (AFI) was assessed. Results. HFUPR did not change significantly between 37 and 42 weeks' gestation. However, HFUPR decreased during the last 14 days prior to the onset of spontaneous labor (P < 0.005). No significant correlation was found between HFUPR and AFI, neither when measured at the same time nor when HFUPR and AFI were measured at various intervals in time. Conclusion. HFUPR falls before and in relation to the time of onset of labor rather than in relation to gestational age.

Omphalocele: comparison of outcome following prenatal or postnatal diagnosis

OBJECTIVES

To assess the impact of prenatal compared with postnatal diagnosis on outcome for liveborn infants with an isolated or with a non-isolated omphalocele.

METHODS

This was a retrospective analysis of 101 prenatally and 45 postnatally diagnosed cases of omphalocele. Cases were collected from the ultrasound database of the Division of Obstetrics and Prenatal Medicine and the patient database of the Department of Pediatric Surgery.

RESULTS

Following confirmation at delivery or autopsy, prenatally diagnosed omphaloceles included 21 isolated cases, 44 non-isolated cases with a normal karyotype and 36 non-isolated cases with an abnormal karyotype. Of the prenatally diagnosed apparently isolated cases (n = 31), 12 (39%; 95% CI, 22-58%) revealed associated anomalies after delivery. Liveborn infants with an isolated omphalocele had significantly worse short-term morbidity following prenatal diagnosis (n = 14) compared with diagnosis at birth (n = 29), having a lower gestational age at delivery, lower Apgar scores, longer duration of ventilation and parenteral nutrition, more readmissions and a longer hospital stay. The prenatally diagnosed subset contained more infants with a giant omphalocele (9/14 vs. 3/29, P = 0.001) and liver herniation (8/14 vs. 6/29, P = 0.02). The outcome of liveborn infants with a non-isolated omphalocele diagnosed prenatally (n = 17) was not different from that of those diagnosed at birth (n = 16), except for a greater need for ventilation and parenteral nutrition in the prenatal subset.

CONCLUSION

When counseling patients with a prenatal diagnosis of isolated omphalocele, it is important to remember that over one third could turn out to have associated anomalies. Liveborn infants with an isolated omphalocele detected prenatally have worse short-term morbidity than do cases detected at birth. Those with non-isolated omphaloceles detected prenatally have an increased need for ventilation and parenteral nutrition compared with those detected at birth.

Pre- and postnatal diagnosis and outcome of fetuses and neonates with esophageal atresia and tracheoesophageal fistula

OBJECTIVES

Clinical symptoms and ultrasound signs during pregnancy could suggest the presence of esophageal atresia (EA). However, most often EA is diagnosed postnatally. The aim of our study is to evaluate the course and outcome for prenatally and postnatally diagnosed EA. In addition, we studied the outcome of isolated versus nonisolated EA.

METHODS

In a retrospective data analysis, ultrasound characteristics, maternal and neonatal variables as well as clinical outcome were compared for fetuses/neonates with prenatal (n = 30) or postnatal (n = 49) diagnosis of EA. Clinical outcome in terms of morbidity and mortality of isolated EA was compared with that of EA complicated by chromosomal or structural anomalies.

RESULTS

Prenatally diagnosed children were born 2 weeks earlier than postnatally diagnosed children (36.4 weeks vs 38.2 weeks; P = 0.02). The former had higher mortality rates (30 vs 12%; P = 0.05) and more associated anomalies (80 vs 59%; P = 0.04). In both subsets, there was a high morbidity rate in the survivors (not significant). Nonisolated EA was associated with greater occurrence of polyhydramnios (53 vs 27%; P = 0.04) and higher mortality rate (28 vs 0%; P = 0.002).

CONCLUSIONS

Mortality was significantly higher in prenatally diagnosed infants and in infants with additional congenital anomalies. Isolated EA is associated with good outcome.

Differences in amniotic fluid patterns and fetal biometric parameters in third trimester pregnancies with and without diabetes

OBJECTIVE

The amniotic fluid index (AFI) has been increasingly used in the assessment of fetal well-being. We conducted the study to evaluate and compare the amniotic fluid index in third trimester normal and diabetic human pregnancy and to assess the correlation between the AFI and the fetal biometric parameters.

METHODS

Real-time ultrasound was performed to evaluate the AFI (four-quadrant technique), and to measure the biparietal diameter, head circumference, abdominal circumference, and femur length in 225 normal and 120 diabetic pregnant women from 27 to 42 weeks of gestation. Each patient was studied only once.

RESULTS

AFI in normal pregnancies was less than that in diabetic pregnancies throughout the gestational ages studied (27-42 weeks). In normal pregnancy, the mean AFI was 14.0 cm at 27 weeks and decreased to 11.4 cm at 42 weeks (r = 0.25, p = 0.0005), whereas in diabetic pregnancies, the values remained stable throughout the gestational ages studied. There exist significant differences in AFI, estimated fetal weight, estimated fetal weight %, abdominal circumference, abdominal circumference %, and head circumference to abdominal circumference ratio between the two groups. In both normal and diabetic pregnancies, there is a positive correlation between the AFI and the percentile of abdominal circumference (p < 0.0001), and between the AFI and the percentile of estimated fetal weight (p < 0.0001).

CONCLUSION

This study provides gestational age-specific values of the AFI in normal and diabetic pregnancies. Diabetic pregnancy has greater AFI values than normal pregnancy between 27 and 42 weeks. The AFI correlates to the percentile of the estimated fetal weight and the abdominal circumference in both groups, suggesting that there may be a relationship between increased AFI and large for gestational age fetus independent of diabetes.

Isolated or non-isolated duodenal obstruction: perinatal outcome following prenatal or postnatal diagnosis

OBJECTIVES

To determine whether the pre- or postnatal diagnosis of either isolated or non-isolated duodenal obstruction (DO) is associated with different outcomes.

METHODS

A single-center retrospective analysis was carried out of 91 cases diagnosed with a DO between January 1991 and June 2003. Data on the diagnosis, treatment and outcomes of the cases were gathered, and differences between the groups were analyzed.

RESULTS

Twenty-eight cases of DO were diagnosed before and 63 after birth. Of 15 presumed isolated cases in the prenatally diagnosed group, four revealed associated or chromosomal anomalies after birth. The types of obstruction present were significantly different between the prenatally (n = 11) and postnatally (n = 27) detected subsets of isolated DO. The prenatally detected subset displayed a lower median gestational age at delivery, lower median birth weight and a higher prematurity rate (8/11 vs. 8/27). The diagnosis of DO occurred significantly later in the postnatally detected subset than the postnatal confirmation of the diagnosis in the prenatally detected cases. In the non-isolated cases of DO, no difference was found in the type of chromosomal or associated anomaly or the type of obstruction between the prenatally detected (n = 17) and postnatally detected subsets (n = 36). Trisomy 21 was present in 7/17 (41%) vs. 22/36 (61%) cases, respectively. Two terminations and three intrauterine deaths occurred in the prenatal non-isolated subset. The liveborn infants from the prenatally detected non-isolated subset (n = 12) showed a significantly higher prematurity rate (9/12 vs.14/36), lower median birth weight and earlier confirmation of diagnosis after delivery. After surgery, outcome was similar between both subsets of isolated and non-isolated DO. All the infants with an isolated DO survived. Neonatal death occurred in three prenatally and five postnatally diagnosed cases with non-isolated DO.

CONCLUSIONS

The outcome of prenatally and postnatally diagnosed DO is not essentially different despite more prematurity and a lower birth weight in the former. Of the prenatally detected cases of DO assumed to be isolated, 25% revealed additional chromosomal or associated anomalies after delivery, which influenced outcome.

How well do the amniotic fluid index and single deepest pocket indices (below the 3rd and 5th and above the 95th and 97th percentiles) predict oligohydramnios and hydramnios?

OBJECTIVE

This study was undertaken to determine whether the amniotic fluid index (AFI) and single deepest pocket percentiles can reliably identify a dye-determined amniotic fluid volume.

STUDY DESIGN

Ultrasound measurements and dye-determined volumes were prospectively collected. Oligohydramnios predictors included AFI and single deepest pocket below the 3rd and 5th percentiles, and hydramnios predictors were based on AFI and single deepest pocket above the 95th and 97th percentiles.

RESULTS

Two hundred ninety-one women with singleton pregnancies participated, including 75 pregnancies (26%) with oligohydramnios and 31 pregnancies (10%) with hydramnios. The predictive ability of the AFI and single deepest pocket indices (<3rd and 5th percentiles) to identify oligohydramnios was between 11% and 27% and to identify hydramnios (>95th and 97th percentiles) ranged between 33% and 46%. The best prediction was for normal fluid volume with an accuracy of 83% to 94%.

CONCLUSION

Amniotic fluid indices perform best for the identifying normal AF volumes, whereas the identification of oligohydramnios or hydramnios is poor.

Fetal karyotyping after 28 weeks of gestation for late ultrasound findings in a low risk population

OBJECTIVE

To analyze the indications and the results of invasive testing for fetal karyotyping for ultrasound abnormality in the third trimester of pregnancy, when first- and second-trimester screening tests were negative.

METHODS

Retrospective study of 171 consecutive pregnancies that underwent invasive testing after 28 weeks of gestation in 2 institutions between January 1999 and December 2001. Forty-one patients did not have any form of screening for fetal aneuploidy beforehand. One hundred and thirty of them had a normal first-trimester scan and a low risk of fetal aneuploidy by nuchal translucency and/or maternal serum screening and were included in the statistical analysis.

RESULTS

Mean maternal age, gestational age at diagnosis and at invasive testing were 30.5 years; 29.3 weeks and 32.5 weeks respectively. Amniocentesis and fetal blood sampling were performed in 97 and 33 cases respectively. The most frequent indications for invasive testing in the third trimester were major fetal malformations (51%) and intrauterine growth restriction (19%) detected on routine second- or third-trimester ultrasound examination. Ultrasound markers of aneuploidy and polyhydramnios accounted for 17 and 11% of the indications respectively. Fetal karyotype was normal in 121/130 cases. A gene mutation was found in one case. The karyotype was abnormal in nine cases, including seven cases of aneuploidy (one Turner syndrome, three trisomy 18, and three trisomy 21) and two cases of structural chromosomal abnormalities (46,XX, del 4 p16.1 and 46,XX, dup1). One hundred cases resulted in the delivery of a normal baby. Thirty cases led to termination of pregnancy or intrauterine death due to major fetal malformations (N = 25), abnormal karyotype in six of these, and severe IUGR (N = 5) with normal karyotype. Fetal US markers of aneuploidy and isolated polyhydramnios were associated with a favorable outcome in all cases.A significant increase in the risk of chromosomal anomaly was seen when two or more anomalies were found, rising from 2% with one anomaly to 21% when two or more anomalies were present.

CONCLUSION

In low risk patients, fetal karyotyping in the third trimester may be justified when the diagnosis of fetal malformation is made in the third trimester of pregnancy. Two or more anomalies increase the risk of fetal aneuploidy even with a negative-screening test in the first and second trimester of pregnancy.

The amniotic fluid index in late pregnancy

OBJECTIVE

Our purpose was to examine changes in the amniotic fluid index (AFI) in accurately dated term pregnancies both in relation to gestational age and in relation to the onset of spontaneous labor.

STUDY DESIGN

This was a prospective observational study in 137 women with uneventful term pregnancies, in whom 220 AFI measurements were performed. More than one AFI value was available from 51 individuals.

RESULTS

The AFI did not change significantly between 37 and 42 weeks' gestation, but a significant reduction was seen during the last 11 days before the spontaneous onset of labor (R = -0.37, n = 83, p < 0.001). The AFI (corrected for gestational age) within individuals remained stable over periods of up to 2 weeks. Meconium staining of the amniotic fluid was related to gestational age, but not to the AFI or fetal distress at birth. No significant correlation was found between fetal distress and the AFI, or between fetal distress and the reduction in AFI during the last two measurements before labor.

CONCLUSIONS

The reduction of the AFI in pregnancies progressing beyond term is related to the labor process itself rather than to the exact gestational age.

Is there a relationship between fetal weight and amniotic fluid index?

OBJECTIVE

To establish whether there is a relationship between the amniotic fluid index and estimated fetal weight in the third trimester. The presence of a relationship would require adjustment of amniotic fluid index to take account of estimated fetal weight with potential improvement in its prediction of adverse perinatal outcomes.

METHODS

Paired measurements of amniotic fluid index and estimated fetal weight from 274 low-risk pregnancies enrolled in a longitudinal study of fetal growth. Measurements were made at fortnightly intervals from 30 weeks' gestation until delivery. A relationship between amniotic fluid index and estimated fetal weight was sought at gestational age week intervals of 30-32, 33-35, 36-38 and 39-41.

RESULTS

One thousand and three pairs of measurements of amniotic fluid index and estimated fetal weight were available for analysis. Mean amniotic fluid index decreased towards term as expected. There was no correlation between amniotic fluid index and estimated fetal weight. Furthermore, there was no correlation between amniotic fluid index and estimated fetal weight at any of the gestational age intervals.

CONCLUSIONS

There is no clinically relevant correlation between amniotic fluid index and estimated fetal weight. It should remain clinical practice to take account of gestational age when interpreting amniotic fluid index but it is not necessary to make adjustments for estimated fetal weight.

Monitoring of fetuses with intrauterine growth restriction: a longitudinal study

OBJECTIVE

To describe the time sequence of changes in fetal monitoring variables in intrauterine growth restriction and to correlate these findings with fetal outcome at delivery.

METHODS

This was a prospective longitudinal observational multicenter study on 110 singleton pregnancies with growth-restricted fetuses after 24 weeks of gestation. Short-term variation of fetal heart rate, pulsatility indices of fetal arterial and venous Doppler waveforms and amniotic fluid index were assessed at each monitoring session. The study population was divided into two groups: Group 1 comprised pregnancies with severely premature fetuses, which were delivered < or =32 weeks and Group 2 included pregnancies delivered after 32 completed weeks. Logistic regression was used for modeling the probability for abnormality of a variable in relation to the time interval before delivery. Trends over time were analyzed for all variables by multilevel analysis.

RESULTS

Ninety-three (60 in Group 1 and 33 in Group 2) fetuses had at least three data sets (median, 4; range, 3-27) and had the last measurements taken within 24 h of delivery or intrauterine death. The percentage of abnormal test results and the degree of abnormality were higher in Group 1 compared to Group 2. Amniotic fluid index and umbilical artery pulsatility index were the first variables to become abnormal, followed by the middle cerebral artery, aorta, short-term variation, ductus venosus and inferior vena cava. In Group 1, short-term variation and ductus venosus pulsatility index showed mirror images of each other in their trend over time. Perinatal mortality was significantly higher if both variables were abnormal compared to only one or neither being abnormal (13/33 (39%) vs. 4/60 (7%); P = 0.0002; Fisher's exact test).

CONCLUSION

Ductus venosus pulsatility index and short-term variation of fetal heart rate are important indicators for the optimal timing of delivery before 32 weeks of gestation. Delivery should be considered if one of these parameters becomes persistently abnormal.

Doppler studies on the fetal renal artery in the severely growth-restricted fetus

OBJECTIVES

To examine changes with time in the fetal renal circulation by Doppler sonography in the severely growth-restricted preterm fetus during the period of gradual deterioration prior to delivery, and to examine the relationship between Doppler measurements, amniotic fluid index, birth weight and fetal condition at birth.

METHODS

This was a prospective observational study in 16 preterm growth-restricted fetuses between 26 and 35 weeks of gestational age. Serial Doppler measurements were made of the renal artery, umbilical artery, middle cerebral artery and ductus venosus.

RESULTS

The pulsatility index in the renal artery did not show any correlation with cord blood pH, birth weight or amniotic fluid index corrected for gestational age (Delta/SDAFI). However, peak systolic velocities in the renal artery showed a significant reduction with time (n = 7, P < 0.05) and a significant correlation with: venous cord pH at delivery (n = 12, r = 0.84, P < 0.001), Delta/SDAFI (n = 16, r = 0.67, P < 0.01), and birth weight (n = 16, r = 0.61, P < 0.02). Birth weight correlated significantly with: Delta/SDAFI (n = 15, r = 0.57, P < 0.05), pulsatility index values of the middle cerebral artery (n = 15, r = -0.61, P < 0.02), and pulsatility index values of the ductus venosus (n = 16, r = 0.55, P < 0.05), and Delta/SDAFI correlated significantly with: pulsatility index values of the ductus venosus (n = 15, r = 0.51, P < 0.05) and arterial cord pH values at delivery (n = 8, r = 0.78, P < 0.05).

CONCLUSIONS

Progressive redistribution of the circulation occurs with deterioration of the fetal condition in the growth-restricted preterm fetus. On spectral Doppler this is reflected by changes in peak systolic velocities, but not by changes in pulsatility values of the fetal renal artery waveforms.

Effect of fetal presentation on the amniotic fluid index

OBJECTIVE

The aim of this study was to determine whether the amniotic fluid index differs according to whether a fetus is in breech or cephalic presentation.

STUDY DESIGN

Between January 1995 and April 1996 the amniotic fluid index was measured both immediately before and after attempted external cephalic version. Amniotic fluid indexes were measured by a senior obstetric resident or attending physician. Preprocedure amniotic fluid indexes and change in amniotic fluid index after successful and failed external cephalic version were compared with unpaired and paired Student t tests, respectively. P <.05 was considered statistically significant.

RESULTS

Thirty consecutive women between 36 and 40 weeks' gestation with breech presentations were evaluated before undergoing an attempt at external cephalic version. The preprocedure amniotic fluid index was not different (P =.61) between women who had success (12.1 cm) and failure (11.4 cm) of attempts at external cephalic version. Successful external cephalic version was associated with a statistically significant increase (P <.0001) in amniotic fluid index with respect to gestations with a persistent breech presentation (3.14 vs -0.35).

CONCLUSION

Successful version from a breech to a cephalic presentation resulted in a significant increase in the amniotic fluid index. This should be considered when a breech presentation with a low normal amniotic fluid index is evaluated. Presentation of the fetus should be considered in evaluating amniotic fluid index distribution curves.

The fetal outcome in pregnancies with isolated reduced amniotic fluid volume in the third trimester

Our aim was to assess the outcome of pregnancies where oligohydramnios, defined by a published gestational reference range for amniotic fluid index, was the only abnormal finding at third trimester scan, and all other ultrasound parameters including biometry were within normal limits at initial scan. A retrospective case-control study was performed at The Liverpool Maternity Hospital. 103 pregnancies with reduced amniotic fluid index in the third trimester and apparently normal fetal growth profile ultrasonographically were identified from ultrasound reports throughout 1993. Pregnancies in the third trimester with normal amniotic fluid index on index scan were also identified from these reports and 103 were matched for parity, gestational age at delivery, mode of onset of labour, presentation at labour and medical conditions. Exclusion criteria were ruptured membranes, fetal abnormalities, estimated fetal weight below the fifth centile at index scan and multiple pregnancies. The outcome criteria were birthweight, Apgar scores at delivery, induction and emergency delivery for fetal reasons and admission to Neonatal Intensive Care Unit. Statistical analysis was performed by Fisher's exact test and Gart's odds ratio. Compared with controls, pregnancies in the reduced liquor group had a higher number of babies below the 5th centile (odds ratio 5.2, 95% confidence interval 1.6 to 22), a higher risk of induction for fetal reasons (odds ratio 34.4, 95% confidence interval 5.35 to 1425.5) and admission to Neonatal Intensive Care Unit (odds ratio 9.77, 95% confidence interval 1.3 to 432). Any observed difference in the need for emergency delivery due to fetal reasons was not clinically significant (odds ratio 2.16, 95% confidence interval 0.77 to 6.6) The definition used for oligohydramnios used in this study appears to identify a group of babies with a fourfold risk of low birthweight and a high risk of admission to the Neonatal Intensive Care Unit and induction of labour for fetal reasons. This would suggest that pregnancies with isolated oligohydramnios require some form of fetal monitoring and further prospective studies are required to determine the most appropriate method.

Fetal growth retardation and second trimester maternal serum human chorionic gonadotrophin levels

Second trimester maternal serum human chorionic gonadotrophin (hCG) levels in women who remained normotensive but delivered an unexplained growth retarded infant were compared with those from a control group and a group of women who developed pre-eclampsia in a retrospective observational study. Our hypothesis was that the similar placental pathological changes shared by unexplained normotensive IUGR and pre-eclampsia would be reflected by elevated maternal serum hCG levels in the second trimester. Normotensive women delivering unexplained singleton growth retarded infants were identified (n=43) and their second trimester hCG levels, taken as part of antenatal screening for Down's syndrome, were obtained. These were compared with a control group of 625 women, and a group of 48 women who subsequently developed pre-eclampsia. There was no significant difference in the hCG levels expressed as multiples of the median (MOM) between the women who delivered growth retarded fetuses (median MOM 0.96) and the control group (median MOM 0.97). The levels of hCG in the women who subsequently developed pre-eclampsia were significantly higher (median MOM 1.3, P=0.008). There were no significant differences in AFP levels in the three groups; however, the trend was towards a higher level of AFP in the fetal growth retardation group. Maternal serum hCG in the second trimester does not appear to be elevated in normotensive women who later produce a growth retarded fetus, although human chorionic gonadotrophin levels are significantly higher in women who subsequently develop pre-eclampsia.

A randomised comparison between amniotic fluid index and maximum pool depth in the monitoring of post-term pregnancy

OBJECTIVE

To compare the impact of two different ultrasound methods for assessing amniotic fluid volume on the incidence of obstetric interventions in post-term pregnancies.

DESIGN

A prospective randomised controlled trial.

SETTING

Liverpool Women's Hospital.

PARTICIPANTS

Five hundred women with singleton, uncomplicated pregnancies with gestational age > or = 290 days.

INTERVENTIONS

Random allocation to fetal monitoring by either: 1. amniotic fluid index and computerised cardiotocography, or 2. maximum pool depth and computerised cardiotocography.

MAIN OUTCOME MEASURES

Primary: caesarean section. Secondary: the number of abnormal monitoring tests, induction of labour, intrapartum management and neonatal outcome.

RESULTS

The number of abnormal amniotic fluid indices was significantly higher than the number of abnormal maximum pool depths (10% vs 2.4%; OR 4.51, 95% CI 1.82-11.21; P = 0.0008) which resulted in more inductions for abnormal post-term monitoring in the amniotic fluid index group (14.8% vs 8.4%; OR 1.89; 95% CI 1.07-3.33; P = 0.0362) and more intrapartum electronic fetal monitoring (94.4% vs 88.4%; OR 2.21; 95% CI 1.13-4.29; P = 0.0255). There were no other statistically significant differences in outcomes related to labour and delivery, but there was a trend towards more caesarean sections in the amniotic fluid index group (18.8% vs 13.2%), in particular caesarean sections for fetal distress (8% vs 4%). There were no perinatal deaths and no statistically significant differences in perinatal outcome between the two groups.

CONCLUSIONS

Published reference ranges for amniotic fluid index overestimate the number of abnormal results in post-term pregnancies. Their use, when compared with maximum pool depth, is likely to increase the number of obstetric interventions with, as yet, an uncertain impact on perinatal mortality and morbidity. It is possible that antepartum fetal assessment in pregnancies where the risk of adverse perinatal outcome is very low may cause, rather than prevent morbidity.

A randomised controlled trial of simple compared with complex antenatal fetal monitoring after 42 weeks of gestation

OBJECTIVE

To compare the impact on perinatal outcome of two different protocols for antenatal fetal monitoring after 42 weeks gestation.

DESIGN

A prospective randomised controlled trial.

SETTING

Liverpool Maternity Hospital.

SUBJECTS

One hundred and forty-five women with singleton, uncomplicated pregnancies after 42 weeks of gestation.

INTERVENTIONS

Random allocation to fetal monitoring by either: 1. a modified biophysical profile comprising of computerised cardiotocography, amniotic fluid index, and assessment of fetal breathing, tone and gross body movements; or 2. standard cardiotocography and maximum pool depth.

OUTCOME MEASURES

Cord pH at delivery, number of abnormal monitoring tests, intrapartum management, mode of delivery and neonatal outcome.

RESULTS

There were significantly more abnormal antenatal monitoring results in the modified biophysical profile group (47.2% vs 20.5%; odds ratio = 3.5, 99% CI = 1.3-9.1). There were no differences in cord blood gases, neonatal outcome, or in outcomes related to labour and delivery between the two groups, but a trend towards more obstetric interventions in the modified biophysical profile group was noted. Amniotic fluid volume after 42 weeks was more likely to be labelled as abnormal with amniotic fluid index than with maximum pool depth (44.4% vs 15.1%; odds ratio = 4.5, 99% CI = 1.6-12.8).

CONCLUSIONS

The results suggest that after 42 weeks fetal monitoring with the modified biophysical profile does not improve pregnancy outcome as measured by umbilical cord pH, but is more likely to yield an abnormal result. The higher incidence of abnormal monitoring results in the modified biophysical profile group was likely to be caused by different methods of amniotic fluid assessment in the modified biophysical profile group (amniotic fluid index) and simple monitoring group (maximum pool depth). The use of amniotic fluid index as a test of fetal wellbeing in prolonged pregnancy may lead to more obstetric interventions with, as yet, unclear impact on the perinatal outcome.

Assessment of fetal activity and amniotic fluid volume in the prediction of intrauterine infection in preterm prelabor amniorrhexis

OBJECTIVE

Our purpose was to assess fetal activity, fetal heart rate patterns, and amniotic fluid volume in the prediction of intrauterine infection in pregnancies complicated by preterm prelabor amniorrhexis.

STUDY DESIGN

A prospective study was performed on 89 patients with preterm prelabor amniorrhexis undergoing fetal blood and amniotic fluid sampling for microbiologic investigations. Within 2 hours before cordocentesis and amniocentesis, computerized fetal heart rate monitoring was carried out and ultrasonographic examination was performed for assessment of biophysical profile and amniotic fluid volume.

RESULTS

In the pregnancies with microbiologic evidence of intrauterine infection compared with those with no infection, there was a tendency for a lower biophysical profile score and amniotic fluid index and an increased fetal heart rate. However, in the majority of pregnancies with positive amniotic fluid or fetal blood cultures the results of the various tests were normal.

CONCLUSION

In pregnancies complicated by preterm prelabor amniorrhexis assessment of fetal activity and amniotic fluid volume do not provide useful prediction of intrauterine infection.