Longitudinal measurement of amniotic fluid index in postterm pregnancies and its association with fetal outcome.

Objective: Our purpose was to study the association between dynamic changes in serial amniotic fluid index measurements and adverse fetal outcome in postterm pregnancies.
Study Design: Serial amniotic fluid index values were obtained semiweekly in 139 reliably dated, uncomplicated, singleton pregnancies at > 41 weeks' gestation. Adverse fetal outcome was defined by the presence of moderate or thick meconium, fetal heart rate decelerations, cesarean delivery for fetal distress, neonatal intensive care unit admission, and perinatal mortality.
Results: Prominent changes in the amniotic fluid index (i.e., > 50% increase or decrease) had no association with adverse fetal outcome irrespective of rate of change, provided the final value remained > 5.0 cm. A significant association with fetal heart rate decelerations and the presence of meconium was detected only in patients whose final amniotic fluid index was < or = 5.0 cm (p = 0.007 and p = 0.003, respectively).
Conclusion: Irrespective of the rate of change in amniotic fluid index, postterm pregnancies are significantly associated with potential complications such as fetal heart rate decelerations and meconium staining when the final amniotic fluid index is < or = 5.0 cm.