- Objective: To determine if hydramnios at term gestation is an independent risk factor for poor pregnancy outcome and perinatal death. Study design: The study population consisted of 60 702 patients with singleton gestation who delivered at term (>37 weeks). Patients were classified into two groups according to the presence or the absence of hydramnios. Hydramnios was diagnosed in the presence of an amniotic fluid index greater than 25 cm or of a maximum vertical pocket of amniotic fluid of at least 8 cm or by subjective assessment. Logistic regression analysis was used to evaluate the unique contribution of hydramnios to fetal death and to perinatal and maternal morbidity. Results: The prevalence of hydramnios was 1211/60 702 (2%). Patients with hydramnios had a higher incidence of complications than those with a normal amount of amniotic fluid: cesarean section (22.8 vs. 8.5%, P<0.01), antepartum death (0.6 vs. 0.2%, P<0.005), postpartum death (2.8 vs. 0.4%, P<0.01), abruptio placenta (0.9 vs. 0.3%, P<0.001), fetal distress (6.1 vs. 3.65%, P<0.0015), meconium-stained amniotic fluid (17.8 vs. 15%, P<0.001), low Apgar score at 5 min (2.95 vs. 1%, P<0.01), malpresentation (6.8 vs. 2.9%, P<0.01), clinical chorioamnionitis (0.3 vs. 0.1%, P<0.05), prolapse of cord (2.2 vs. 0.3%, P<0.01), and large-for-gestational-age infant (LGA) (23.8 vs. 8.1%, P<0.01). When adjusted for confounding variables, the presence of hydramnios remained strongly associated with perinatal mortality (odds ratio 5.5 (95% CI 3.2–9.3)) and neonatal and maternal morbidity (odds ratios 2.1 (CI 1.1–3.7) and 2.3 (CI 1.9–2.7), respectively). Conclusions: (1) Hydramnios at term is an independent risk factor for perinatal death; (2) Fetal surveillance is warranted in patients with hydramnios even in the absence of other known risk factors for adverse pregnancy outcome.