The impact of amniotic fluid volume assessed intrapartum on perinatal outcome

Oligohydramnios at term in the high-risk population - how severe is severe?

OBJECTIVES

The term oligohydramnios is linked to pregnancy complications. We previously presented the outcome of the low-risk population (no pregnancy complications) with term oligohydramnios. This study aims to address the high-risk group (Any maternal complication during pregnancy, such as gestational diabetes, pre-gestational diabetes, chronic hypertension, preeclampsia, anemia, asthma, obesity, and multi parity.).

METHODS

This retrospective cohort study of 1,114 singleton term (≥37), oligohydramnios (AFI <50 mm) pregnancies from Shamir Medical Center between 2017 and 2021. Compering the low-risk to high-risk groups with subdivision by severity of oligohydramnios.

RESULTS

A total of 211 subjects (19 %) were high-risk cases and 903 (81 %) low-risk cases. Comparing these two groups, subjects of the high-risk group were older (31.34 ± 5.85 vs. 29.51 vs. 4.96), had earlier gestational age at delivery 39.53 ± 1.18 vs. 40, had higher mean AFI (35 ± 12.7 vs. 33 ± 14.5), were subject to more labor inductions (81 vs. 69.7 %), and CS rate (19.9 vs. 12.4 %). Logistic regression revealed a need for more cesarean sections in the high-risk group. Additionally, more labor inductions and a higher risk of negative fetal outcomes.

CONCLUSIONS

This study highlights the importance of considering pregnancy risk factors when we are approaching oligohydramnios in high-risk pregnancies.

Amniotic fluid volume and pregnancy outcomes in twin pregnancies: A systematic review and meta-analysis

Objective

To analyse amniotic fluid volume (AFV), specifically oligohydramnios or polyhydramnios, and associated pregnancy and neonatal outcomes in twin gestations through systematic review and meta-analysis.

Methods

We utilised systematic review methodology to identify items within published and grey literature resources. Prospective and retrospective studies with a control group were included. Inclusion criteria were as follows: studies in English, twin pregnancy in which AFVs and associated pregnancy and/or neonatal outcomes were evaluated. Exclusion criteria included the presence of an anomalous fetus, chromosome abnormality, monochorionic diamniotic twin pregnancy complicated by twin-twin transfusion syndrome or twin-reversed arterial perfusion, twin gestations undergoing therapeutic interventions (i.e. fetoscopic laser photocoagulation and serial amniocentesis) and monochorionic monoamniotic twin pregnancy.

Results

The literature search identified 1068 abstracts, only four met criteria for inclusion and analysis. The pooled data (two studies per outcome) revealed no significant difference in rate of pre-term delivery (OR: 2.94; CI: 0.20-43.81), pre-term delivery less than 32 weeks (OR: 1.97; CI: 0.43-9.12), umbilical cord pH < 7 (OR: 2.66; CI: 0.22-32.51), rate of stillbirth (OR: 4.13; CI: 0.40-42.70), neonatal death (OR: 1.48; CI: 0.05-43.94), rate of NICU admission (OR: 1.38; CI: 0.61-3.11) or rate of small-for-gestational-age (SGA) infants (OR: 1.39; CI: 0.33-5.94).

Conclusion

Based on the pooled data (two studies per outcome), there was no difference in the fate of pre-term delivery, umbilical cord pH < 7, stillbirth, neonatal death or SGA infants. What is disturbing is the lack of studies (1946-2020) that analysed the association between AFV and pregnancy outcomes in twin pregnancies.

Comparison of Perinatal and Maternal Outcomes in Borderline Versus Normal Amniotic Fluid Index in a Tertiary Care Center in Odisha: An Observational Prospective Study

Background

Amniotic fluid is a protective fluid in the amniotic sac of a gravid uterus that serves many crucial functions by becoming part of an indicator of a functioning fetoplacental unit during the intrauterine life of a fetus. The most commonly used method for measuring amniotic fluid is the amniotic fluid index (AFI). In this study, we aimed to investigate the perinatal and maternal outcomes in borderline AFI versus normal AFI.

Methodology

This observational prospective study included 200 pregnant women who were admitted to Pradyumna Bal Memorial Hospital, Bhubaneswar from September 2019 to February 2021. Women with singleton pregnancy in their third trimester were enrolled in this study after applying inclusion and exclusion criteria. Of the included women, 100 were cases with borderline AFI, and 100 were control with normal AFI. Fetal and maternal outcomes were compared between the two groups. Data analysis was done using SPSS version 23 (IBM Corp., Armonk, NY, USA).

Results

Maternal outcomes such as preterm delivery, meconium-stained liquor, and lower segment cesarean section in women with borderline AFI were significantly higher (p ≤ 0.001). The borderline AFI group had a higher rate of perinatal complications such as Apgar score of <7 (p = 0.001), respiratory distress syndrome (p = 0.001), neonatal intensive care unit admission (p <0.001), intrauterine growth restriction (p < 0.001), and low birth weight (p < 0.001).

Conclusions

The borderline AFI group was associated with adverse perinatal and maternal outcomes which were significantly higher in this group compared to the control group. Therefore, patients with borderline AFI should be monitored carefully during the antepartum and intrapartum period.

Hourly fetal urine production rate in isolated oligohydramnios at term

OBJECTIVE

The aim of this study was to evaluate the hourly fetal urine production rate (HFUPR) via three-dimensional ultrasonography in women with isolated oligohydramnios and compare with normal pregnant women at term.

MATERIALS AND METHODS

This was a prospective observational cohort study of 112 women from 34 to 40 6/7 weeks' gestation. They were classified into three groups according to the amniotic fluid index (AFI) and ultrasonographic estimated fetal weight (EFW) as isolated oligohydramnios (defined as AFI below 5% and appropriate EFW corresponding to gestational age) (n = 34) and IUGR (defined as EFW below 5% corresponding to gestational age irrespective amniotic fluid) (n = 17), and normal pregnancy (n = 61). HFUPR was measured using three-dimensional virtual organ computer-aided analysis. Adverse perinatal outcomes in all participants were examined.

RESULTS

There was no significant difference in HFUPR between patients with isolated oligohydramnios and women with normal pregnancies (median, 40.0 mL/h [interquartile range [IQR] 31.0-66.5] vs. 48.6 [31.5-81.2], p = 0.224). HFUPR was significantly decreased in the IUGR group (13.8 mL/h [IQR 10.1-24.8]), compared to the normal pregnancy group (p<0.001) and the isolated oligohydramnios group (p<0.001). HFUPR was significantly decreased in neonates with adverse perinatal outcomes compared to the control (24.7 mL/h [IQR 13.4-47.4] vs. 43.6 [29.8-79.0], p = 0.016).

CONCLUSION

HFUPR was not decreased in patients with isolated oligohydramnios but was decreased in patients with IUGR when compared to normal controls at term.

Amniotic fluid index curves in the obese gravida

OBJECTIVE

To determine whether amniotic fluid volume as measured by amniotic fluid index (AFI) is influenced by maternal pre-gestational obesity as measured by body mass index (BMI).

METHODS

This was a retrospective cohort study of pregnant women between 20 and 43 weeks gestation receiving ultrasounds with AFI measurements at Augusta University Medical Center between 2003 and 2017. A subset of 500 charts that met inclusion and exclusion criteria were reviewed to obtain maternal clinical data. The study cohort was subdivided by maternal BMI at initial obstetric visit into three groups: normal weight (18.5 kg/m2-24.9 kg/m2), overweight (25.0 kg/m2-29.9 kg/m2), and obese (≥ 30 kg/m2). Chi-square analysis was used to compare BMI groups in terms of categorical clinical characteristics and outcome variables, and analysis of variance (ANOVA) was used for continuous variables. Mixed effects regression models (MRMs) were used to evaluate AFI throughout gestation separately in each group, and MRM-based analysis of covariance was used to compare AFI throughout gestation among groups. AFI curves were constructed for the 5th, 50th, and 95th percentiles for all study subjects combined and separately for normal weight, overweight, and obese subjects.

RESULTS

Fitted curves relating AFI percentiles to estimated gestational age (EGA) showed statistically significant differences among BMI groups. There was also a significant difference in AFI over gestation across the obesity groups.

CONCLUSION

Fitted curves for AFI throughout pregnancy showed statistically significant differences among BMI groups.

Determination of reference values for third trimester amniotic fluid index: a retrospective analysis of a large cohort of pregnancies with comparison to previous nomograms

Purpose: To establish a new set of reference values for third-trimester amniotic fluid index (AFI) and compare them to other previously published normograms.Methods: A retrospective cross-sectional cohort analysis of all singleton sonographic evaluations >22 gestational weeks in one university affiliated medical center between 2013 and 2017. Pregnancies complicated by rupture of membranes, major anomalies/chromosomal abnormalities were excluded. One evaluation per patient per pregnancy was randomly selected. Reference values were constructed using a best-fit regression model for estimation of mean and standard deviation at each gestational age after normalization of variables and compared with previously published norms.Results: A total of 7037 ultrasound evaluations entered the analysis. Correlation between AFI and gestational age was best represented by a first-degree polynomial equation. AFI decreased gradually from 16.4 at 22 weeks to 13.3 at 40 weeks (cm, median). The standard deviation increased with gestational age with AFI ranging from 12.9-20.2 at 22 weeks and 4.7-26.2 at 40 weeks (cm, 2.5-97.5 percentile). Compared to other curves, our reference values demonstrated a higher median AFI throughout all gestation.Conclusions: Reference values for the third trimester AFI were established. Curves should be correlated with perinatal outcome prior to wide clinical implementation.

Perinatal outcomes following labor induction with dinoprostone in pregnancies with borderline amniotic fluid index at term: A clinical observation study

AIM

To compare perinatal outcomes of dinoprostone for induced labor in pregnancies with a borderline versus normal amniotic fluid index (AFI) at term, and to investigate the related factors affecting outcomes of cesarean section.

METHODS

The retrospective study was carried out in Hubei Maternal and Child Health Hospital with singleton pregnancies of 37-42 weeks' gestation from January to August 2016. A total of 992 subjects were divided into two groups: borderline AFI group (n =125) with 5 < AFI ≤ 8 and normal AFI group (n = 867) with 8 < AFI ≤ 24.

RESULTS

Time to delivery (P =0.004) and use of oxytocin augmentation (P = 0.011) were significantly lower in pregnancies with borderline AFI. There were no significant differences between the two groups in terms of delivery mode, time to onset of labor, fetal distress, Apgar scores, meconium-stained amniotic fluid, birth weight, or incidences of admission to neonatal intensive care unit (NICU). Gestational hypertension and birth weight were the major factors affecting outcomes of cesarean section in the borderline group (odds ratio [OR] = 13.61, 95% confidence interval [CI] 1.96-94.49, P =0.008 and OR = 1.003, 95% CI 1.001-1.005, P =0.001, respectively). Maternal age (OR = 1.12, 95% CI 1.06-1.19, P < 0.001), parity (OR = 7.57, 95% CI 3.05-18.76, P < 0.001), biparietal diameter (OR = 0.55, 95% CI 0.33-0.91, P = 0.021), and meconium-stained amniotic fluid (OR = 1.56, 95% CI 1.12-2.17, P = 0.009) were related factors in the normal group.

CONCLUSION

The perinatal outcomes of dinoprostone for induced labor are comparable between the two groups. Gestational hypertension and birth weight are factors related to outcomes of cesarean section in the borderline group.

Perinatal outcomes in uncomplicated late preterm pregnancies with borderline oligohydramnios

PURPOSE

The purpose of this study is to determine the adverse perinatal outcomes in uncomplicated late preterm pregnancies with borderline oligohydramnios.

METHODS

A total of 430 pregnant women with an uncomplicated singleton pregnancy at a gestational age of 34 + 0-36 + 6 weeks were included. Borderline oligohydramnios was defined as an amniotic fluid index (AFI) of 5.1-8 cm, which was measured using the four-quadrant technique. Adverse perinatal outcomes were compared between the borderline and normal AFI groups.

RESULTS

Approximately 107 of the 430 pregnant women were borderline AFI, and 323 were normal AFI. The demographic and obstetric characteristics were similar in both groups. Delivery <37 weeks, cesarean delivery for non-reassuring fetal heart-rate testing, meconium-stained amniotic fluid, Apgar 5 min <7, transient tachypnea of the newborn, respiratory distress syndrome, neonatal intensive care unit, and hyperbilirubinemia were not statistically different between the groups (p = .054, p = .134, p = .749, p = 0.858, p = .703, p = .320, p = .185, and p = .996, respectively). Although gestational age was full-term, induction of labor rates were significantly higher in the borderline AFI group (p = .040). In addition, fetal renal artery pulsatility index pulsatility index (PI) was significantly lower in the borderline AFI group than in the normal AFI group (p = .014).

CONCLUSION

Our results indicated that borderline AFI was not a risk for adverse perinatal outcomes in uncomplicated, late preterm pregnancies.

Perinatal outcomes with isolated oligohydramnios at term pregnancy

AIMS

To compare the outcomes of term gestations with oligohydramnios in the absence of other underlying disorders and term gestations with normal amniotic fluid.

METHODS

A retrospective analysis of obstetric outcomes in 27,708 term pregnancies. We compared three groups: labor induced because of oligohydramnios, spontaneous onset of labor with normal amniotic fluid, and labor induced because of late term pregnancy with normal amniotic fluid. We excluded pregnancies with maternal or fetal diseases or disorders potentially related with amniotic fluid alterations. The main outcome measures were mode of delivery, neonatal birth weight, umbilical artery blood pH, Apgar scores and neonatal discharge status.

RESULTS

Compared to spontaneous labor, induction of labor because of oligohydramnios was associated with a higher risk of cesarean delivery and small size of the fetus for gestational age (SGA). Compared to induction because of late term pregnancy there were no significant differences in neonatal, although neonates had a higher risk of being SGA.

CONCLUSION

The only perinatal outcome for which the risk was higher in term pregnancies with isolated oligohydramnios was SGA. The systematic induction of labor in these pregnancies should be questioned.

Antenatal fetal surveillance "Assessment of the AFV"

The evaluation of amniotic fluid volume (AFV) is an established part of the antenatal surveillance of pregnancies at risk for an adverse pregnancy outcome. The two most commonly used ultrasound techniques to estimate AFV are the amniotic fluid index (AFI) and the single deepest pocket (SDP). Four studies have defined normal AFVs, and although their normal volumes have similarities, there are also differences primarily due to the statistical methodology used in each study. Dye-determined AFV correlates with ultrasound estimates for normal fluid volumes but correlates poorly for oligohydramnios and polyhydramnios. The addition of color Doppler in estimating AFV leads to the overdiagnosis of oligohydramnios. Neither the AFI nor the SDP is superior in identifying oligohydramnios, but the SDP is a better measurement choice as the use of AFI increases the diagnosis rate of oligohydramnios and labor inductions without an improvement in pregnancy outcomes.

Borderline amniotic fluid index and perinatal outcomes in the uncomplicated term pregnancy

OBJECTIVE

To determine perinatal outcomes in uncomplicated term pregnancies with a borderline amniotic fluid index (AFI).

METHODS

A retrospective review was conducted of uncomplicated singleton pregnancies at term (>37 weeks). Borderline and normal AFI were defined as 5.1 ≤ AFI ≤ 8.0 cm and 8.1 ≤ AFI ≤ 24 cm, respectively. Adverse perinatal outcomes, cesarean delivery for non-reassuring fetal heart rate testing, meconium-stained amniotic fluid, a 5-min Apgar score of <7, admission to the neonatal intensive care unit (NICU), and whether the neonate was small for gestational age were compared between the borderline and normal AFI groups.

RESULTS

Borderline AFI was not significantly associated with cesarean delivery for non-reassuring fetal heart rate testing (p = 0.513), meconium-stained amniotic fluid (p = 0.641), admission to the NICU (p = 0.368), or a 5-min Apgar score of <7 (p = 1.00). However, the number of neonates who were small for gestational age (p = 0.021) and rates of induction of labor (p < 0.001) were significantly higher in the borderline group. Multiple logistic regression analysis showed that borderline AFI was not associated with cesarean delivery for non-reassuring fetal heart rate testing (odds ratio [OR] = 0.72, 95% confidence interval [CI] 0.27-1.91, p = 0.52).

CONCLUSION

In uncomplicated term pregnancies, a borderline AFI does not increase the risk of adverse perinatal outcomes.

Borderline amniotic fluid index and its relation to fetal intolerance of labor: a 2-center retrospective cohort study

OBJECTIVES

To determine whether a borderline amniotic fluid index (AFI) in the third trimester is associated with an increased rate of cesarean delivery for fetal intolerance of labor, meconium-stained amniotic fluid, and intrauterine growth restriction, among other adverse perinatal outcomes.

METHODS

Patients with a diagnosis of a borderline AFI between January 2008 and August 2012 were identified. Antepartum, delivery, and neonatal data were collected and compared to a cohort with a normal AFI.

RESULTS

We enrolled 739 patients, including 177 with a borderline AFI (>5 and <10 cm) and 562 with a normal AFI (≥ 10-24 cm); 360 patients delivered at University of Arizona Medical Center, and 379 delivered at St Joseph's Hospital. Combined and individual analyses of each center revealed no significant difference in fetal intolerance of labor (P = .19) or cesarean delivery for fetal intolerance (P = .074) between cohorts. In both settings, patients with a borderline AFI were more likely than those with a normal AFI to undergo antepartum testing (P < .001). A statistically significant increase in intrauterine growth restriction in the borderline AFI group was noted, with a calculated risk ratio of 13.76 (P < .001). There was no difference between groups for meconium-stained amniotic fluid (P = .23), neonatal intensive care unit admission (P = .054), preterm delivery (P = .31), or operative vaginal delivery (P = .45).

CONCLUSIONS

The findings of this study suggest that there is no difference in the rate of fetal intolerance of labor in pregnancies with a borderline AFI and those with a normal AFI. Pregnancies complicated by a borderline AFI are more likely to undergo antepartum testing, yet the benefit is unclear. Significantly more patients with a borderline AFI had underlying growth restriction, which may provide a useful tool for risk stratification in the management of a borderline AFI.

Correlation of amniotic fluid index with perinatal outcome

OBJECTIVES

We aimed to evaluate the predictive value of amniotic fluid index (AFI) (<5) for adverse perinatal outcome in terms of cesarean section for fetal distress, birth weight, meconium staining, Apgar scores, and cord pH at birth.

METHODS

This was a prospective study of 200 antenatal women booked at Ram Manohar Lohia (RML) Hospital during the years 2009-2011 with gestational age between 34 and 41 weeks. The women's history, clinical examination recorded, and AFI were measured and the perinatal outcome was compared between two groups, i.e., AFI < 5 and >5.

RESULTS

The cesarean section rate for fetal distress and low birth weight babies, <2.5 kg, was higher in patients with oligohydramnios (p = 0.048, 0.001, respectively). There was no significant difference in meconium staining, Apgar score at 5 min <7, and cord pH at birth between the two groups (p = 0.881, 0.884, 0.764, respectively).

CONCLUSIONS

Oligohydramnios has a significant correlation with cesarean section for fetal distress and low birth weight babies.

Amniotic fluid as a vital sign for fetal wellbeing

Introduction: Amniotic fluid, once thought to merely provide protection and room for necessary movement and growth for the fetus, is now understood to be a highly complex and dynamic system that is studied as a data point to interpret fetal wellbeing. Methods: Assessment of amniotic fluid volume is now routine when performing a sonographic evaluation of fetal status and is an important consideration in the assessment and management of perinatal morbidity and mortality.1,2 In this review, we will cover the dynamics that affect amniotic fluid volume, review methods for measurement and quantification of volume, review definitions for normative data as related to neonatal outcomes, and provide evidence based guidance on the workup and management options for oligoydramnios and polyhydramnios in singleton and twin pregnancies. Conclusions: When abnormalities of fluid exist, appropriate workup to uncover the underlying etiology should be initiated as adverse fetal outcomes are sometimes associated with these variations from normalcy.

The effects of intravenous hydration on amniotic fluid volume and pregnancy outcomes in women with term pregnancy and oligohydramnios: a randomized clinical trial

INTRODUCTION

Amniotic fluid is an important factor in the prediction of fetal survival. The aim of this research was to evaluate the effects of intravenous hydration of mothers on amniotic fluid volume and in turn on pregnancy outcomes.

METHODS

The current single blind controlled clinical trial was conducted on 20 pregnant mothers with amniotic fluid index of lower or equal to 5 cm and gestational age of 37-41 weeks. The subjects were divided into two groups of case and control through simple random sampling. Amniotic fluid index was measured in all participants. The case group received one liter of isotonic saline during 30 minutes by the bolus method. Reevaluations of amniotic fluid index in both groups were made 90 minutes after baseline measurement. Independent t-test and paired t-test were used to compare the two groups and mean amniotic fluid index before and after treatment, respectively.

RESULTS

Hydration of mothers significantly increased the amniotic fluid index in the case group (mean change: 1.5 cm; 95%CI: 0.46 - 2.64; P = 0.01). The mean change of amniotic fluid index in the control group did not significantly increase (P = 0.06). The elevation of amniotic fluid index in the hydration group (32%) was significantly higher than the control group (1%) (P = 0.03).

CONCLUSION

In this study intravenous hydration increased amniotic fluid index of mothers with term pregnancy and oligohydramnios. Since it caused no complications for the mother and the fetus, it can be used as an effective method in management of oligohydramnios.

Short-term outcome among term singleton infants with intrapartum oligohydramnios

AIM

To evaluate rates of early short-term neonatal complications among term singleton newborn infants with oligohydramnios.

METHODS

Retrospective data were collected on 456 term infants with prenatal diagnosis of oligohydramnios and on matched controls, including information on maternal condition and on infant perinatal complications.

RESULTS

Infants in the study group were born with lower birthweight and were SGA compared with those in the control group. Rates of renal malformations were significantly higher in the study group compared with the controls (15-3.3% and 3-0.7%, respectively; p = 0.007). Among the severe oligohydramnios subgroup (Amniotic Fluid Index <2), renal anomalies were even more prevalent compared to other infants with oligohydramnios and to the controls (6-9.8%, 9-2.3% and 3-0.7%, respectively; p < 0.001). The incidence of skeletal deformities (developmental dislocation of hip and torticollis) was higher among the study group.

CONCLUSION

Term infants with oligohydramnios that was detected near birth are associated with a greater prevalence of renal malformations (mostly mild hydronephrosis) as well as congenital torticollis and developmental dislocated hips compared with controls. Postnatal renal evaluation should be considered in infants with severe oligohydramnios.

A nationwide survey of risk factors for stillbirth in Taiwan, 2001-2004

OBJECTIVE

The purpose of this study was to evaluate the nationwide stillbirth rate and explore the potential risk factors associated with stillbirths.

PATIENTS AND METHODS

Data from vital registrations during the time period from January 1, 2001 through to December 31, 2004 in Taiwan were used. Stillbirth was defined as fetal death with more than 20 completed weeks' gestational age (GA) or with birth weight more than 500 g if the GA was not known.

RESULTS

There were a total of 8481 stillbirths identified nationwide between January 1, 2001 and December 31, 2004. The stillbirth rate was nine per 1000 total births in the study period, and the proportionate decline was nearly 48.8% in the most recent decade. There was a significant increase in average maternal age during this period. Advanced maternal age and teenage pregnancy were independent significant risk factors for stillbirths even after accounting for the effects of medical conditions that were more likely to occur among these particular age groups. Those fetuses that had been exposed to cord prolapse, maternal cervical incompetence and oligohydramnios/polyhydramnios were especially vulnerable. By contrast, women who had foreign nationality, fetal ultrasound surveys, fetal heart beat monitoring and hastened parturition were less likely to have stillbirth.

CONCLUSION

The stillbirth rate in Taiwan has remained high despite advancements in medical care. Prenatal evaluation of high risk women may decrease the adverse fetal outcomes.

A prospective clinical study of feto-maternal outcome in pregnancies with abnormal liquor volume

AIMS AND OBJECTIVE(S): Evaluating feto-maternal outcome in pregnancies with abnormal liquor volume.

MATERIAL AND METHOD(S)

200 pregnant subjects between 20 and 42 weeks of gestation, who were clinically suspected to have an abnormal amniotic fluid volume (oligohydramnios or polyhydramnios) were subjected to ultrasonographic (USG) assessment of amniotic fluid index. The subjects were closely monitored through pregnancy, labour and puerperium.

OBSERVATION(S)

Ultrasonically, abnormal liquor volume was confirmed in 90-93% clinically suspected patients. Post term pregnancy (38.5%), PROM (30%) and prolonged pregnancy (23.5%) were associated with oligohydramnios. Fetal congenital anomalies (31.1%), diabetes mellitus (20%), PIH (17.7%), twin pregnancy (6.6%) and Rh incompatibility (4.4%) were associated with polyhydramnios. The incidence of labour induction, fetal labour intolerance, CS for fetal distress and 1 min Apgar of <7 was high in oligohydramnios subjects. Premature labour complicated 40% of polyhydramnios pregnancies. The overall incidence of congenital anomalies (14%) and perinatal mortality (20%) in subjects with abnormal liquor volume was significantly higher (P < 0.001) than in women with normal liquor volume (0.3, 2.3% respectively).

CONCLUSION(S)

A good clinical examination can pick up most subjects of abnormal liquor volume. Abnormal liquor volumes are associated with increased maternal morbidity and adverse perinatal outcome.

Amniotic fluid and the clinical relevance of the sonographically estimated amniotic fluid volume: oligohydramnios

The amniotic fluid volume (AFV) is regulated by several systems, including the in-tramembranous pathway, fetal production (fetal urine and lung fluid) and uptake (fetal swallowing), and the balance of fluid movement via osmotic gradients. The normal AFV across gestation has not been clearly defined; consequently, abnormal volumes are also poorly defined. Actual AFVs can be measured by dye dilution techniques and directly measured at cesarean delivery; however, these techniques are time-consuming, are invasive, and require laboratory support, and direct measurement can only be done at cesarean delivery. As a result of these limitations, the AFV is estimated by the amniotic fluid index (AFI), the single deepest pocket, and subjective assessment of the AFV. Unfortunately, sonographic estimates of the AFV correlate poorly with dye-determined or directly measured amniotic fluid. The recent use of color Doppler sonography has not improved the diagnostic accuracy of sonographic estimates of the AFV but instead has led to overdiagnosis of oligohydramnios. The relationship between the fixed cutoffs of an AFI of 5 cm or less and a single deepest pocket of 2 cm or less for identifying adverse pregnancy outcomes is uncertain. The use of the single deepest pocket compared to the AFI to identify oligohydramnios in at-risk pregnancies seems to be a better choice because the use of the AFI leads to an increase in the diagnosis of oligohydramnios, resulting in more labor inductions and cesarean deliveries without any improvement in peripartum outcomes.

Borderline or marginal amniotic fluid index and peripartum outcomes: a review of the literature

The predictive accuracy of a borderline amniotic fluid index (AFI) for an adverse pregnancy outcome is uncertain. Pregnancy outcomes of a borderline versus normal AFI suggest an increased risk of meconium-stained fluid, intrauterine growth restriction, cesarean delivery for a nonreassuring fetal heart rate, low Apgar scores, and neonatal intensive care unit admission with borderline fluid. These results are inconclusive because of study design variations, the absence of receiver-operating characteristic curves, our inability to calculate likelihood ratios, and a lack of randomized trials. There is currently insufficient evidence to recommend additional antenatal testing delivery based on a borderline AFI. Sonography could be considered for evaluating fetal growth until a definitive association or lack of an association between a borderline AFI and intrauterine growth restriction/small size for gestational age can be determined.

Reducing stillbirths: screening and monitoring during pregnancy and labour

BACKGROUND

Screening and monitoring in pregnancy are strategies used by healthcare providers to identify high-risk pregnancies so that they can provide more targeted and appropriate treatment and follow-up care, and to monitor fetal well-being in both low- and high-risk pregnancies. The use of many of these techniques is controversial and their ability to detect fetal compromise often unknown. Theoretically, appropriate management of maternal and fetal risk factors and complications that are detected in pregnancy and labour could prevent a large proportion of the world's 3.2 million estimated annual stillbirths, as well as minimise maternal and neonatal morbidity and mortality.

METHODS

The fourth in a series of papers assessing the evidence base for prevention of stillbirths, this paper reviews available published evidence for the impact of 14 screening and monitoring interventions in pregnancy on stillbirth, including identification and management of high-risk pregnancies, advanced monitoring techniques, and monitoring of labour. Using broad and specific strategies to search PubMed and the Cochrane Library, we identified 221 relevant reviews and studies testing screening and monitoring interventions during the antenatal and intrapartum periods and reporting stillbirth or perinatal mortality as an outcome.

RESULTS

We found a dearth of rigorous evidence of direct impact of any of these screening procedures and interventions on stillbirth incidence. Observational studies testing some interventions, including fetal movement monitoring and Doppler monitoring, showed some evidence of impact on stillbirths in selected high-risk populations, but require larger rigourous trials to confirm impact. Other interventions, such as amniotic fluid assessment for oligohydramnios, appear predictive of stillbirth risk, but studies are lacking which assess the impact on perinatal mortality of subsequent intervention based on test findings. Few rigorous studies of cardiotocography have reported stillbirth outcomes, but steep declines in stillbirth rates have been observed in high-income settings such as the U.S., where cardiotocography is used in conjunction with Caesarean section for fetal distress.

CONCLUSION

There are numerous research gaps and large, adequately controlled trials are still needed for most of the interventions we considered. The impact of monitoring interventions on stillbirth relies on use of effective and timely intervention should problems be detected. Numerous studies indicated that positive tests were associated with increased perinatal mortality, but while some tests had good sensitivity in detecting distress, false-positive rates were high for most tests, and questions remain about optimal timing, frequency, and implications of testing. Few studies included assessments of impact of subsequent intervention needed before recommending particular monitoring strategies as a means to decrease stillbirth incidence. In high-income countries such as the US, observational evidence suggests that widespread use of cardiotocography with Caesarean section for fetal distress has led to significant declines in stillbirth rates. Efforts to increase availability of Caesarean section in low-/middle-income countries should be coupled with intrapartum monitoring technologies where resources and provider skills permit.

Abnormal Doppler velocimetry is related to adverse perinatal outcome for borderline amniotic fluid index during third trimester

AIM

To evaluate the relationship between abnormal Doppler velocimetry and adverse perinatal outcomes in pregnancies with borderline amniotic fluid index (AFI).

METHODS

Medical records of 3740 pregnancies with known AFI and Doppler velocimetry measurements within 2 weeks of delivery, and delivered between January 1996 and December 2003, were retrospectively analyzed. Borderline AFI was defined as 5 cm < AFI < or = 8 cm. For the umbilical artery, Doppler velocimetry was considered abnormal when the S/D ratio was greater than 3.0 or when end-diastolic flow was absent; whereas, for the uterine artery, the S/D ratio was greater than 2.6 or presence of end-systolic notch was defined as abnormal. Adverse perinatal outcomes (small for gestational age, cesarean section for fetal distress, 5 min Apgar score of less than 7, respiratory distress syndrome, NICU admission, and perinatal death) according to Doppler velocimetry in borderline AFI were evaluated.

RESULTS

Compared to the normal AFI group (n = 3523), the borderline AFI group (n = 217) had significantly higher incidence of adverse perinatal outcome (28.8% vs 54.8%). There was 3-fold increase in the incidence of adverse perinatal outcome among women with the borderline AFI in comparison to normal AFI (OR, 3.00; CI, 2.27-4.00). When abnormal Doppler velocimetry was associated with borderline AFI, a 5-fold increase in the incidence of adverse perinatal outcome was noted (OR, 5.26; CI, 3.00-9.21).

CONCLUSION

In the borderline AFI group, the presence of abnormal Doppler velocimetry measurement was related to increased risk of adverse perinatal outcome. Thus, borderline AFI of 5-8 cm, especially when associated with abnormal Doppler velocimetry, mandates closer antenatal surveillance.

Induction of labor and perinatal outcome: the impact of the amniotic fluid index

OBJECTIVE

The purpose was to determine the impact of the amniotic fluid index on the perinatal outcome of patients admitted for induction of labor at term.

STUDY DESIGN

Patients (n=180) included in the study were those admitted for induction of labor at 37-42 weeks' gestation, with unfavorable cervix and intact membranes. The amniotic fluid index (AFI) was determined in all patients using the four-quadrant technique within 24 h of the induction of labor. Patients were divided into two groups based on their AFI: the oligohydramnios group with AFI < or = 5 cm (n = 66) and a normal group with AFI > 5 cm (n = 114). The perinatal outcomes of the two groups were compared.

RESULTS

The two groups were similar with regard to maternal age, gestational age, and birth weight. Meconium staining of the amniotic fluid was significantly higher in the group with AFI < or = 5 cm (p = 0.040). The number of cesarean deliveries due to fetal distress was significantly higher even after adjusting for other confounding factors in the group with AFI < or = 5 cm (adjusted OR 6.52 [95% CI 1.82, 23.2]; p < or = 0.0001). There was no significant difference between the two groups with regard to Apgar scores or neonatal admission.

CONCLUSION

Induction of labor at term in patients with oligohydramnios is associated with an increased risk of cesarean delivery due to fetal distress.

A randomized clinical trial of the intrapartum assessment of amniotic fluid volume: amniotic fluid index versus the single deepest pocket technique

OBJECTIVE

The purpose of this study was to determine whether an intrapartum assessment of amniotic fluid identifies a pregnancy that is at risk for an adverse outcome.

STUDY DESIGN

Parturients who were admitted for delivery were assigned randomly to have the amniotic fluid assessed either by amniotic fluid index or by the presence of a 2 x 1 pocket.

RESULTS

The amniotic fluid index was obtained in 499 pregnancies, and the 2 x 1 technique was performed in 501. Oligohydramnios was diagnosed in 25% of amniotic fluid index pregnancies versus 8% with the use of the 2 x 1 pocket technique (P <.001). Both techniques failed to identify patients who underwent an amnioinfusion for fetal distress (P=.864) or who experienced variable (P=.208) or late decelerations (P=.210) that influenced delivery, fetal distress in labor (P=.220), caesarean delivery for fetal distress (P=.133), and admission to neonatal intensive care unit (P=.686).

CONCLUSION

Neither the amniotic fluid index nor the 2 x 1 pocket technique that was undertaken as a fetal admission test identifies a pregnancy that is at risk for an adverse outcome.

An amniotic fluid index < or =5 cm within 7 days of delivery in the third trimester is not associated with decreasing umbilical arterial pH and base excess

OBJECTIVE

To determine if an amniotic fluid index (AFI) < or =5.0 cm within 7 days of delivery in the third trimester is associated with decreasing umbilical arterial pH and base excess.

STUDY DESIGN

Cases for this retrospective cohort study were all pregnancies > or =26 weeks with intact membranes and an AFI < or =5.0 cm within 7 days of delivery between 11/99 and 7/02. Multiple gestations, aneuploid, and anomalous fetuses were excluded. Controls with an AFI >5.0 cm within 7 days of delivery were matched to each case within 1 week by gestational age. For a control group with a mean+/-SD umbilical arterial pH of 7.26+/-0.07 and alpha=0.05, a sample size of 100 would have a power of 99% to detect a difference with a study group whose mean was 7.20. Data were compared using paired Student's t-test, Mann-Whitney, Fisher's exact, chi(2) and risk ratios with 95% confidence intervals.

RESULTS

In all, 131 neonates with an AFI < or =5.0 cm were matched to 131 controls with an AFI >5 cm. There was no difference in gestational age (37.6+/-3.0, 37.7+/-3.0 weeks) or birth weight (2897+/-810, 2762+/-788 g). There was no difference in umbilical artery pH (7.25+/-0.07, 7.26+/-0.07) or base excess (-3.32+/-2.59, -2.83+/-2.45 mmol/l), even in small for gestational age (SGA) infants in both groups. There was no difference in the number of SGA neonates, 5-minute Apgar <7, respiratory distress syndrome, necrotizing enterocolitis, or neurologic morbidity. Linear regression showed no correlation between AFI and either umbilical arterial pH (r=-0.00047, SE=0.001, p=0.63) or base excess (r=-0.029, SE=0.037, p=0.428).

CONCLUSION

An AFI < or =5.0 cm measured within 7 days of delivery in the third trimester is not associated with decreasing umbilical arterial pH and base excess.

Misoprostol for Cervical Ripening and Labor Induction in Pregnancies with Oligohydramnios

The efficacy and safety of misoprostol for cervical ripening and labor induction in patients with oligohydramnios was investigated. 57 pregnancies with oligohydramnios and 58 cases with a normal amniotic fluid volume (controls) were enrolled in this prospective trial. All patients received 50 microg of intravaginal misoprostol every 5 h. Primary outcomes were: cesarean section rate; induction to delivery time; oxytocin augmentation; uterine hyperstimulation; meconium passage; fetal heart rate (FHR) changes; fetal distress requiring delivery, and Apgar scores. There were no differences in the mean time to delivery, cesarean section rate, oxytocin augmentation or Apgar scores. The mean induction to delivery time in oligohydramnios and control groups were, 11 h 43 min and 11 h 18 min, respectively (p > 0.05). FHR changes were observed in 26.3% of oligohydramnios group and 32.7% of control group (p > 0.05). There was no statistically significant difference in the cesarean section rate and the uterine hyperstimulation between the 2 groups. These data suggest that misoprostol can be used as an effective agent for cervical ripening and labor induction in pregnancies with oligohydramnios without increasing the risk for perinatal outcome, compared to those with normal amniotic fluid volumes.

Predictability of intrapartum and neonatal outcomes with the amniotic fluid volume distribution: a reassessment using the amniotic fluid index, single deepest pocket, and a dye-determined amniotic fluid volume

OBJECTIVE

The purpose of this study was to establish whether ultrasound-estimated or dye-determined amniotic fluid distribution (upper compared with lower quadrant) is predictive of perinatal outcome.

STUDY DESIGN

Amniotic fluid distribution as measured by the amniotic fluid index, single deepest pocket, and dye-determined volumes was ascertained and correlated with intrapartum and neonatal outcomes.

RESULTS

Between January 1997 and January 2001, 135 women (70 upper-greater and 65 lower-greater) participated in this prospective observational study. The sum of the amniotic fluid index (P =.309), single deepest pocket (P =.168), and dye-determined amniotic fluid volume (P =.368) for the upper-greater compared with the lower-greater groups were similar. Decelerations in labor (P =.597), late decelerations (P =.999), cesarean deliveries for fetal distress (P =.413), and umbilical cord pH < 7.2 were similar (P =.647)

CONCLUSION

Ultrasound-estimated and dye-determined amniotic fluid volumes are similar between upper-greater and lower-greater groups, and intrapartum/neonatal outcomes are not affected by the amniotic fluid distribution.

Ultrasound estimation of amniotic fluid volume using the largest vertical pocket containing umbilical cord: measure to or through the cord?

OBJECTIVES

The purpose of this investigation was to determine the preferable method, either measuring to the umbilical cord or through the umbilical cord to the base of the pocket, of ultrasonically estimating amniotic fluid volume.

SUBJECT AND METHODS

This was a prospective study carried out in singleton pregnancies undergoing a third-trimester amniocentesis. The amniotic fluid index (AFI) and single deepest pocket (SDP) were measured prior to amniocentesis. If measured spaces contained umbilical cord, measurements were made to and through the cord. Actual amniotic fluid volume was determined by the dye-dilution technique.

RESULTS

One-hundred pregnancies were evaluated. Low dye-determined volume was identified in a significantly greater number of pregnancies using the AFI to the cord (7/28, 25%) compared to through the cord (2/28, 7%) (P = 0.025). The SDP technique to the cord was superior in low volumes (2/28, 7%) vs. (0/28, 0%) through the cord (although statistical significance could not be determined because there were no low through-the-cord measurements).

CONCLUSIONS

For the detection of low amniotic fluid volumes, the AFI to the cord is better than through the cord. Measurement to the cord and through the cord had similar accuracy for both the AFI and SDP techniques in normal and high dye-determined amniotic fluid volumes.

Amniotic fluid index in low-risk pregnancy as an admission test to the labor ward

BACKGROUND

Oligohydramnios has been shown to be a predictor of intrapartal fetal distress. In a selected group of low-risk pregnancies, however, it has not yet been established that oligohydramnios contributes to intrapartal fetal distress.

METHODS

Ultrasonically estimated four-quadrant amniotic fluid index as a test for admission to the labor ward was evaluated as a predictive factor for fetal distress during labor in a prospective "blind" study comprising 600 low-risk pregnancies. Oligohydramnios was defined as an amniotic fluid index < or = 50 mm. The parturients were divided into two groups according to the status of the fetal membranes. The amniotic fluid index results were correlated to fetal outcome: Apgar score at 1 and 5 min, pH of blood in umbilical artery and vein, operative delivery because of fetal distress, cesarean delivery because of fetal distress, and number of babies referred to the neonatal intensive care unit.

RESULTS

Two-hundred and sixty-seven women had ruptured membranes. Among these a significant increase in operative delivery because of fetal distress was seen in cases of oligohydramnios compared with the normal amount of amniotic fluid (odds ratio 3.86, confidence interval = 1.25-11.9). No significant differences were seen regarding other variables of perinatal outcome. The group with intact membranes comprised 333 parturients. Among these, no significant differences in perinatal outcome could be seen in relationship to the amniotic fluid index, although a 50% increase in emergency operations for fetal distress was seen in women with oligohydramnios. A significant correlation might have been evident even in that group if a larger sample had been studied.

CONCLUSION

The results indicate that measurement of the amniotic fluid index in low-risk pregnant women admitted for labor might identify parturients with an increased risk of intrapartal fetal distress.

A diminished intrapartum amniotic fluid index is a predictive marker of possible adverse neonatal outcome when associated with prolonged labor

OBJECTIVE

To determine whether a diminished intrapartum amniotic fluid volume represents a risk of adverse neonatal outcome when it occurs in conjunction with prolonged labor.

METHODS

The intrapartum amniotic fluid index (iAFI) was measured in 242 parturients over 35 weeks of gestation during 1st-stage labor, and the umbilical artery blood gas was analyzed at delivery. The subjects were divided into group A (n = 99), having a diminished amniotic fluid volume (iAFI < or = 8.0 cm) and group B (n = 143), having a normal amniotic fluid volume (iAFI 8.1-20.0 cm), and selected antenatal, delivery, and neonatal variables were compared. In addition, the two groups were subdivided according to the duration of labor. Statistical analysis was performed using independent Student's t test, Mann-Whitney U test, chi-square analysis, and Fisher's exact test where appropriate. p < 0.05 was considered significant.

RESULTS

The patient characteristics and pregnancy outcomes were similar in groups A and B, as were the incidences of an umbilical artery blood pH <7.20 and/or an Apgar score <7 (group A 9.5%, group B 10.1%). In group A, however, the incidence of an adverse neonatal outcome was 23.5% in cases in whom the duration of labor was longer than 8 h which was significantly higher than in cases in whom the duration of labor was 8 h or less (2.8%; p < 0.01). In group B, the incidence of an adverse neonatal outcome was similar in the two subgroups.

CONCLUSIONS

The risk of an adverse neonatal outcome is higher in patients with diminished amniotic fluid volume if labor is prolonged. Consequently, determination of the iAFI could be a useful admission test.

Use of prostaglandin E2 for cervical ripening in pregnancies with oligohydramnios

The effectiveness of intracervical prostaglandin E2 (PGE2) was studied in 96 primigravidas with unfavorable cervix and need for induction of labor. Group A consisted of 49 oligohydramnios and group B of 47 cases with normal amniotic fluid volume (controls). A single dose of 0.5 mg PGE2 gel was applied intracervically and several parameters were recorded during the next hours. The mean number of uterine contractions increased during the first 2 h in both groups, decreased during the next one and did not change significantly afterwards. The mean fetal heart rate (FHR) in group A decreased during the first 2 h and then increased, staying always within normal limits. The mean FHR in group B increased for 2 h, decreased during the next hour and did not change significantly afterwards. No significant differences were found between the two groups regarding mode of delivery, Apgar score and neonatal acidosis. Intracervical PGE2 appeared to effectively stimulate cervical ripening and labor induction in oligohydramnios, without causing side effects to the uterus and fetus.

Perinatal outcome of oligohydramnios without associated premature rupture of membranes and fetal anomalies

To investigate the perinatal outcome of patients with oligohydramnios (amniotic fluid index < or = 5 cm), but without premature rupture of membranes and fetal congenital anomalies, data from 245 singleton pregnancies were analyzed and compared to those with normal amniotic fluid volumes (5 < amniotic fluid index < 24 cm, n=27,261). Significantly higher incidences of primiparity, pregnancy-induced hypertension, premature separation of placenta, past history of intrauterine fetal death, past history of preterm delivery, postterm pregnancy, and advanced maternal age were noted to be associated with the occurrence of oligohydramnios. Pregnancies complicated by a markedly diminished amniotic fluid volume assessed antenatally by ultrasound were significantly more frequently associated with adverse perinatal outcomes such as preterm delivery, low or very low birth weight, low Apgar scores, intrauterine fetal death, small-for-gestational-age newborns, meconium staining, cesarean delivery, neonatal intensive care, and neonatal death.

The amniotic fluid index, single deepest pocket, and two-diameter pocket in normal human pregnancy

OBJECTIVE

This study was undertaken to determine normative values for amniotic fluid index, single deepest pocket, and 2-diameter pocket across gestation.

STUDY DESIGN

Fifty patients with normal pregnancies at each gestational age between 14 and 41 weeks' gestation were recruited prospectively and scanned once. Data were transformed into logarithmic (base 10) values for analysis. Polynomial regression equations were used to predict the normal values for amniotic fluid index, single deepest pocket, and 2-diameter pocket across gestational age and to predict the weekly percentage changes.

RESULTS

The mean amniotic fluid index, single deepest pocket, and 2-diameter pocket values were significantly lower among patients at <37 weeks' gestation (n = 1150) than among those at > or =37 weeks' gestation (n = 250; P <.001 for all comparisons). The calculated prevalences of oligohydramnios (amniotic fluid index < or =5 cm, single deepest pocket <2 cm, or 2-diameter pocket <15 cm(2)) were significantly different (P <.0001) for the three techniques (8%, 1%, and 30%, respectively). Hydramnios (amniotic fluid index >24 cm, single deepest pocket >8 cm, or 2-diameter pocket >50 cm(2)) was also diagnosed with significantly different (P <.0001) frequencies (0%, 0.7%, and 3%, respectively).

CONCLUSIONS

This is the largest prospective study to date to provide normative data for each of three ultrasonographic techniques used to assess amniotic fluid volume. The single deepest pocket appears to be the preferable method, because its use is least likely to lead to the false-positive diagnosis of either oligohydramnios or hydramnios.

Pregnancy outcomes after antepartum diagnosis of oligohydramnios at or beyond 34 weeks' gestation

OBJECTIVE

Our purpose was to assess whether antepartum oligohydramnios is associated with adverse perinatal outcomes.

STUDY DESIGN

Women delivered between July 1, 1991, and September 30, 1996, who underwent ultrasonography at >/=34 weeks' gestation were analyzed. Oligohydramnios was defined as an amniotic fluid index </=50 mm. Perinatal outcomes in pregnancies with oligohydramnios were compared with those with an amniotic fluid index of >50 mm.

RESULTS

In our analysis of 6423 pregnancies, 147 (2.3%) were complicated by oligohydramnios. This complication was associated with increased labor induction (42% vs 18%; P <.001), stillbirth (1. 4% vs 0.3%; P <.03), nonreassuring fetal heart rate (48% vs 39%; P <. 03), admission to the neonatal intensive care nursery (7% vs 2%; P <. 001), meconium aspiration syndrome (1% vs 0.1%; P <.001), and neonatal death (5% vs 0.3%; P <.001).

CONCLUSION

Antepartum oligohydramnios is associated with increased perinatal morbidity and mortality.

Perinatal outcome and amniotic fluid index in the antepartum and intrapartum periods: A meta-analysis

OBJECTIVE

Our purpose was to perform a meta-analysis of studies on the risks of cesarean delivery for fetal distress, 5-minute Apgar score <7, and umbilical arterial pH <7.00 in patients with antepartum or intrapartum amniotic fluid index >5.0 or <5.0 cm.

STUDY DESIGN

Using a MEDLINE search, we reviewed all studies published between 1987 and 1997 that correlated antepartum or intrapartum amniotic fluid index with adverse peripartum outcomes. The inclusion criteria were studies in English that associated at least one of the selected adverse outcomes with an amniotic fluid index of </=5.0 cm versus >5.0 cm. Contingency tables were constructed for each study, and relative risks and standard errors of their logs were calculated. Fixed-effects pooled relative risks were calculated for groups of studies that were homogeneous, whereas random-effects pooled relative risks were calculated for significantly heterogeneous groups of studies.

RESULTS

Eighteen reports describing 10,551 patients met our inclusion criteria. An antepartum amniotic fluid index of </=5.0 cm, in comparison with >5.0 cm, is associated with an increased risk of cesarean delivery for fetal distress (pooled relative risk, 2.2; 95% confidence interval, 1.5-3.4) and an Apgar score of <7 at 5 minutes (pooled relative risk, 5.2; 95% confidence interval, 2.4-11.3). An intrapartum amniotic fluid index of </=5.0 cm is also associated with an increased risk of cesarean delivery for fetal distress (pooled relative risk, 1.7; 95% confidence interval, 1.1-2.6) and an Apgar score <7 at 5 minutes (pooled relative risk, 1.8; 95% confidence interval, 1.2-2.7). A poor correlation between the amniotic fluid index and neonatal acidosis was noted in the only study that examined this end point. More than 23,000 patients are necessary to demonstrate that the incidence of umbilical arterial pH <7.00 is 1.5 times higher among those with oligohydramnios in labor than among those with adequate amniotic fluid index (alpha = 0.05; beta = 0.2)

CONCLUSIONS

An antepartum or intrapartum amniotic fluid index of </=5.0 cm is associated with a significantly increased risk of cesarean delivery for fetal distress and a low Apgar score at 5 minutes. There are few reports linking amniotic fluid index and neonatal acidosis, the only objective assessment of fetal well-being. A multicenter study with sufficient power should be undertaken to demonstrate that a low amniotic fluid index is associated with an umbilical arterial pH <7.00.