Reevaluation of the relationship between amniotic fluid volume and perinatal outcome

Ultrasound estimation of amniotic fluid volume (AFI) is a critical component of antenatal surveillance. Alterations in AFI have classically been considered an indication of fetal compromise, but recent studies have called this into question. The present study was undertaken to reevaluate the relationship between AFI and perinatal outcome.

The perinatal data base of the authors' institution was queried for all patients in a 6-year period who had AFI evaluated. Two groups, 1 high-risk and 1 low-risk, were evaluated to determine the relationship between AFI and gestational age. An additional high-risk group that had AFI determined within 48 hours of delivery was also used to correlate AFI with intrapartum and perinatal outcomes. Statistical analysis was performed using linear regression analysis to evaluate the correlation between AFI and gestational age or birth weight. Additional correlations were done using analysis of variance, chi-square, Fisher exact test, or Student t test. Interaction between variables was analyses using logistic regression analysis.

Fourteen thousand seven hundred forty-seven AFI determinations in 4337 high-risk patients, and 1153 AFI determinations in 1153 low-risk patients were evaluated. There were no clinically significant correlations between AFI and gestational age. In the second high-risk group of 454 patients there was a significant correlation between polyhydramnios and large-for-gestational age infants, congenital anomalies, and an increase in cesarean section for delivery. There was an increased risk of nonreassuring fetal heart rate patterns during labor for the oligohydramnios patient, but only in preterm patients. There was no strong relationship between AFI and neonatal complications or length of stay in the neonatal intensive care unit. Logistic regression confirmed that AFI was not significantly correlated with perinatal outcome.

The present study suggests that AFI is a weaker predictor of perinatal outcome than has been classically suggested. Although the AFI identification of polyhydramnios was helpful in identifying LGA fetuses and fetuses at risk for congenital abnormalities, oligohydramnios was a rather weak predictor of poor perinatal outcome.