Assessing the optimal definition of oligohydramnios associated with adverse neonatal outcomes

Objectives:-The purpose of this study was to compare the use of an amniotic fluid index (AFI) less than 5 cm to the use of an AFI less than the fifth percentile for gestational age in predicting adverse perinatal outcomes. Methods:-This was a retrospective cohort study from 1998 to 2008. Patients with an AFI less than 5 cm and those with an AFI less than the fifth percentile were compared to patients with a normal AFI. The primary outcome measure was neonatal intensive care unit (NICU) admission. Results:-A total of 17,887 patients had complete information for analysis. There were 145 NICU admissions in patients with an AFI less than 5 cm (relative risk, 2.2) compared to 235 in patients with an AFI less than the fifth percentile for gestational age (relative risk, 2.37). The sensitivity and specificity for NICU admission using an AFI less than 5 cm were 10.9% and 95.2% compared to 17.6% and 92.5% for an AFI less than the fifth percentile for gestational age. Conclusions:-Oligohydramnios defined as an AFI less than the fifth percentile better predicts fetuses at risk for adverse perinatal outcomes compared to an AFI less than 5 cm.