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 <= 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.