Amniotic fluid index in the uncomplicated term pregnancy: Prediction of outcome

OBJECTIVE: To establish whether an association between oligohydramnios and pregnancy outcome is present in the uncomplicated term pregnancy. STUDY DESIGN: Pregnancies with a singleton fetus in cephalic presentation at term (≥ 37 weeks), a reactive non-stress test and an anteparturn amniotic fluid index performed within four days of delivery between January 1994 and September 1998 were identified. Excluded were those with any maternal or fetal complication or unavailable outcome information. The primary outcome measure was rate of operative vaginal or abdominal delivery for a nonreassuring fetal heart rate tracing. Statistical analysis included Fisher's exact test and one-way analysis of variance, with a two-tailed P < .05 considered significant. RESULTS: Two hundred thirty-two women met the inclusion criteria; of them, 44 (19%) had an amniotic fluid index ≤ 5 cm. There was no difference in the operative delivery rate for a nonreassuring fetal heart tracing between those with a normal amniotic fluid index > 5 cm vs. ≤5 cm (39 [21%] vs. 5 [11%], P >.05). In addition, there were no differences between the two groups in rates of neonatal intensive care unit admissions or five-minute Apgar scores < 7. Patients with a normal amniotic fluid index had a significantly lower labor induction rate (96 [51%] vs. 42 [98%], P>.001) and higher rate of meconium-stained amniotic fluid (65 [35%] vs. 7 [16%], P = .01) than those with a low amniotic fluid index. CONCLUSION: In the uncomplicated pregnancy at term, an amniotic fluid index ≤ 5 cm increases the incidence of labor induction but does not appear to affect the rate of operative delivery for abnormal fetal heart rate tracings.