OBJECTIVE: Oligohydramnios can be defined by an amniotic fluid index <5th percentile for gestational age or an amniotic fluid index ≤5.0 cm regardless of gestational age. The purpose of this prospective study was to determine whether oligohydramnios by either definition predicts accurately, in a high-risk population, the risks for cesarean section for fetal distress, Apgar score <7 at 5 minutes, and neonatal acidosis.

STUDY DESIGN: An amniotic fluid index was obtained in 490 consecutive parturients with medical or obstetric complications and a reliable gestational age. After each delivery, an umbilical arterial blood gas analysis was obtained. Both measures of amniotic fluid index were rated as screening tests with use of sensitivity, specificity, predictive values, and receiver-operator characteristic curves.

RESULTS: The incidences of cesarean section for fetal distress and umbilical arterial pH <7.00 were 14% and 1.8%, respectively. The 70 neonates delivered by cesarean section for distress, compared with the 420 without, had a significantly higher incidence of pH <7.00 (8.5% vs 0.7%, p = 0.0004, relative risk 5.0, 95% confidence interval 2.9 to 8.4). Sensitivity and positive predictive values of an amniotic fluid index <5th percentile for gestational age to predict pH <7.00 were 0.8% and 22%, respectively, and for an amniotic fluid index ≤5.0 cm, 0.5% and 11%, respectively. Receiver-operator characteristic curves indicate that an amniotic fluid index between 0 and 20 cm cannot predict accurately which parturients will have cesarean sections for distress or be delivered of a newborn with a low Apgar score at 5 minutes or a pH <7.10.

CONCLUSION: Both criteria for oligohydramnios are poor predictors of adverse outcome for high-risk intrapartum patients. (Am J Obstet Gynecol 1997;176:1130-8.)