The underlying cause of polyhydramnios determines prematurity.

The preterm delivery rate in polyhydramnios is higher than in the normal population. We conducted this study to determine if different aetiologies for polyhydramnios have different frequencies of preterm delivery. Three hundred and forty women with a singleton pregnancy and polyhydramnios were included in the study group. A delivery was considered premature if it occurred before 37 weeks' gestation. Preterm deliveries occurred in 14.1 per cent of patients with unexplained polyhydramnios, 27.7 per cent of patients with insulin-dependent diabetes mellitus (IDDM), and in 36 per cent of pregnancies with congenital malformations. The prevalence of preterm delivery was significantly greater for the subgroups with IDDM (P = 0.02) and congenital malformations (P = 0.001), when compared with patients with idiopathic polyhydramnios. The prevalence of preterm delivery in patients with gestational diabetes mellitus was no greater than for the population at large. The underlying cause of polyhydramnios is a major factor in determining when delivery will occur.