The association between isolated oligohydramnios at term and pregnancy outcome

As conflicting data exist concerning the implications of isolated oligohydramnios on pregnancy outcome at term, we aimed to assess this association in low-risk pregnancies.

A retrospective cohort study of term pregnancies with sonographic finding of isolated oligohydramnios (amniotic fluid index (AFI) <5 cm) between 2007 and 2012. Outcome was compared to a control group of pregnancies with normal AFI (5-25 cm). Pregnancies complicated by thrombophilia, hypertension, diabetes, deviant fetal growth or chromosomal/structural abnormalities were excluded. Composite adverse outcome included CS/operative delivery due to non-reassuring heart rate (NRFHR), low Apgar score, umbilical artery pH < 7.10, neonatal intensive care admission, meconium aspiration syndrome, intubation or hypoxic-ischemic encephalopathy.

Overall, 987 pregnancies complicated by isolated oligohydramnios were compared to 22,280 low-risk pregnancies with normal AFI. Isolated oligohydramnios was associated with a higher rate of induction of labor (27.7 vs. 3.7 %, p < 0.001), CS due to NRFHR (2.3 vs. 1.1 %, p < 0.01) and composite adverse outcome (9.7 vs. 7.1 %, p < 0.01). However, after adjusting for potential confounders as induction of labor and nulliparity using multivariable logistic regression analysis, isolated oligohydramnios was not found to be independently associated with increased risk for composite adverse outcome (OR 1.01, 95 % CI 0.80-1.27, p = 0.93).

Isolated oligohydramnios at term by itself is not associated with increased obstetrical morbidity.