Association of isolated polyhydramnios at or beyond 34 weeks of gestation and pregnancy outcome

Objective: To evaluate pregnancy outcome among women with isolated polyhydramnios at admission for labor at or beyond 34 weeks of gestation. Methods: Retrospective cohort study at a tertiary medical center between 2007 and 2012. Isolated polyhydramnios was defined as amniotic fluid index (AFI) greater than 25 cm at admission in the absence of gestational or pregestational diabetes mellitus or fetal structural or chromosomal anomalies. Women with isolated polyhydramnios were compared with women with a normal AFI (5-25 cm). Results: Overall, 31,376 women were eligible for analysis, of whom 215 (0.7%) had isolated polyhydramnios and 31,161 normal AFI. Women with isolated polyhydramnios had higher rates of labor induction (7.9% compared with 4.8%, P.04) and cesarean delivery (12.1% compared with 5.1%, P<.001). They also had higher rates of placental abruption (0.9% compared with 0.2%, P.02), abnormal or intermediate fetal heart rate (FHR) tracings (7.0% compared with 3.2%, P.002), and prolonged first stage of delivery (6.0% compared with 1.4%, P<.001). Isolated polyhydramnios was also associated with higher rates of shoulder dystocia (1.9% compared with 0.3%, P<.001) and respiratory distress syndrome (0.5% compared with 0.03%, P.001). On a multiple logistic regression model, isolated polyhydramnios was an independent risk factor for labor induction (adjusted odds ratio [OR] 1.7, 95% confidence interval [CI] 1.01-2.8), cesarean delivery (adjusted OR 2.6, 95% CI 1.7-4.0), prolonged first stage of delivery (adjusted OR 3.6, 95% CI 1.97-6.7), abnormal or intermediate FHR tracings (adjusted OR 2.6, 95% CI 1.6-4.5), placental abruption (adjusted OR 8.4, 95% CI 2.00-35.4), shoulder dystocia (adjusted OR 3.4, 95% CI 1.2-9.7), and respiratory distress syndrome (adjusted OR 38.9, 95% CI 4.6-332.6). Mild isolated polyhydramnios (AFI 25.1-30.0) was independently associated with cesarean delivery, prolonged first stage of delivery, placental abruption, abnormal or intermediate FHR tracings, and shoulder dystocia. Conclusion: Isolated polyhydramnios at admission for labor at or beyond 34 weeks of gestation is associated with adverse obstetric and neonatal outcomes.