Is amniotic fluid volume status predictive of fetal acidosis at delivery?

Oligohydramnios in complicated and uncomplicated pregnancy: a systematic review and meta-analysis

OBJECTIVE

To evaluate adverse pregnancy outcomes in singleton pregnancies diagnosed with oligohydramnios through a systematic review and meta-analysis of controlled trials.

METHODS

We searched electronic databases via OVID, EBSCO, Web of Science, Google Scholar and others from 1980 to 2015. Prospective and retrospective studies with a control group were included. Two authors independently reviewed the abstracts from the literature search. Inclusion criteria were: studies in English, singleton pregnancy, normal fetal anatomy, intact membranes and oligohydramnios determined by the amniotic fluid index (AFI) technique. We stratified the meta-analysis into two groups according to risk: high risk including studies of oligohydramnios with comorbid conditions (e.g. hypertension) and low risk including studies of isolated oligohydramnios.

RESULTS

Fifteen trials met the inclusion criteria. Nine were high-risk and six were low-risk studies, including 8067 and 27 526 women, respectively. Compared with women with normal AFI, those with isolated oligohydramnios had significantly higher rates of an infant with meconium aspiration syndrome (relative risk (RR), 2.83; 95% CI, 1.38-5.77), Cesarean delivery for fetal distress (RR, 2.16; 95% CI, 1.64-2.85) and admission to the neonatal intensive care unit (NICU) (RR, 1.71; 95% CI, 1.20-2.42). Patients with oligohydramnios and comorbidities were more likely to have an infant with low birth weight (RR, 2.35; 95% CI, 1.27-4.34). However, rates of 5-min Apgar score < 7 (RR, 1.85; 95% CI, 0.69-4.96), NICU admission (RR, 2.09; 95% CI, 0.80-5.45), meconium-stained amniotic fluid (RR, 1.32; 95% CI, 0.62-2.81) and Cesarean delivery for fetal distress (RR, 1.65; 95% CI, 0.81-3.36) were similar to those for women with normal AFI. Stillbirth rates were too low to analyze in the meta-analysis.

CONCLUSIONS

This review helps to delineate which adverse outcomes are increased with oligohydramnios in low-risk pregnancy (NICU admission, Cesarean delivery for fetal distress and meconium aspiration syndrome), but does not provide enough data to determine the optimal timing of delivery in such cases. Oligohydramnios in complicated pregnancy is associated with an increased risk of delivery of an infant with low birth weight, but this may be confounded by the comorbid condition. Therefore, in high-risk pregnancy, management should be dictated by the comorbid condition and not the presence of oligohydramnios. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

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.

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.

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.

Dye-determined amniotic fluid volume and intrapartum/neonatal outcome

OBJECTIVE

To ascertain if a dye-determined amniotic fluid volume was predictive of intrapartum and perinatal outcome.

MATERIALS AND METHODS

The low and normal amniotic fluid volumes (< 5th percentile and > or =5th percentile for gestational age) and the raw dye-determined amniotic fluid distributions were correlated with 10 clinical outcome measures in 74 pregnancies.

RESULTS

In this observational study, median gestational age at delivery was 36 weeks (range 26 to 41) and 16 deliveries were for fetal distress (14 Cesarean and two forceps). There were no differences between the outcomes of pregnancies with low and normal amniotic fluid volumes for any of the clinical outcomes (variable decelerations influencing delivery, p=0.381; late decelerations, p=0.875; Cesarean births for fetal intolerance of labor, p=0.259; intrauterine growth restriction, p=0.998; or umbilical cord arterial pH< 7.2, p=0.259). Analogous results were obtained when the gestational age-adjusted amniotic fluid volumes were compared directly between the pregnancies with normal and abnormal outcomes. There was no difference between the mean amniotic fluid volumes in those pregnancies with variable decelerations influencing delivery (p=0.287), late decelerations (p=0.555), Cesarean births for fetal intolerance of labor (p=0.310), intrauterine growth restriction (p=0.267) or umbilical cord arterial pH< 7.2, and the pregnancies without these intrapartum events. Reduced variability was more commonly observed in pregnancies with higher amniotic fluid volumes (p=0.038, 771 ml, 95% CI 468 to 1269, compared to those without normal variability 444 ml, 95% CI 374 to 526).

CONCLUSIONS

Dye-determined amniotic fluid volume does not appear to be predictive of adverse intrapartum and neonatal 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.