Clinical significance of borderline amniotic fluid index and oligohydramnios in preterm pregnancy

Objective: To estimate pregnancy and neonatal outcomes in women with decreased amniotic fluid index (AFI) between 24 and 34 weeks of gestation, compared with outcomes in those with normal AFI. Methods: This is a review of singleton pregnancies that received ultrasound examinations at 24-34 weeks from 1997 to 2008. If more than one ultrasound examination was performed, the lowest AFI was used for analysis. An AFI 5 cm or less was considered oligohydramnios, 5-8 cm was considered borderline, and more than 8 cm to 24 cm was considered normal. Women with hydramnios or ruptured membranes at time of ultrasound examination were excluded. Results: A total of 28,555 pregnancies met inclusion criteria. Ultrasound examination had been performed to estimate gestational age or evaluate fetal growth in 78%. Major malformations were more common in pregnancies with oligohydramnios and borderline AFI than in those with normal fluid-25%, 10%, and 2%, respectively, P<.001. Among nonanomalous fetuses, complications that occurred more often in pregnancies with oligohydramnios and borderline AFI than in those with normal fluid included preterm birth (62%, 37%, 8%), either indicated (20%, 13%, 2%) or resulting from spontaneous preterm labor (42%, 24%, 6%); cesarean delivery for nonreassuring fetal status (9%, 9%, 4%), and birth weight below the third percentile (37%, 21%, 4%), all P<.001. Conclusion: Pregnancies with decreased AFI between 24 and 34 weeks, including borderline AFI as well as oligohydramnios, were significantly more likely to be associated with major fetal malformations, and in the absence of malformations, to be complicated by fetal growth restriction and preterm birth.