Delivery outcomes of term pregnancy complicated by idiopathic polyhydramnios.

OBJECTIVE: Polyhydramnios is associated with an increased risk of cesarean section. The aetiology of polyhydramnios and the characteristics of the labour may be confounding factors. The objective was to study the characteristics and mode of delivery in case of pregnancy complicated with idiopathic polyhydramnios.

METHODS: This retrospective matched and controlled study included all pregnant women with idiopathic polyhydramnios (amniotic index>25cm or single deepest pocket>8cm) diagnosed at the 2nd or 3rd trimester and persistent at term delivery (>37weeks of pregnancy) in our institution. We excluded pregnancies in which the polyhydramnios could be explained by infection, gestational diabetes, congenital malformation, abnormal karyotype, placental anomalies, alloimmunization as well as pregnancies in which an amniocentesis for the purpose of diagnosis had not been performed. Data were gathered from a tertiary care university hospital register from 1998-2015. Cases of polyhydramnios were matched with the following two women who presented for labour management with spontaneous cephalic presentation, matching for delivery date, maternal age, parity, body mass index. The main outcome measure was the risk of cesarean section. Univariate and multivariate adjusted analysis were performed.

RESULTS: We identified 108 women with idiopathic polyhydramnios and compared them with 216 matched women. Among them, 94 and 188 attempted a trial of labour. Maternal age, mean term delivery and birthweight were 31 years, 39+5weeks gestation and 3550 g. We did not observe differences in maternal characteristics, epidural analgesia and rate of abnormal fetal heart tracing. Induced labour and non-vertex presentations (forehead, bregma, face) were more frequent in the polyhydramnios group (respectively 57.9% versus 27.8%, P<0.05 and 7.8% versus 1%, P<0.05). Cesarean section rate was higher in the case of polyhydramnios in the overall population (45.4% versus 8%, P<0.05) and remained higher after exclusion of cases of induced labour and non-vertex presentation (38.4% versus 3.8%, P<0.05). Amniotomy was more frequent in pregnancies with polyhydramnios (55.8% versus 39.1%, P<0.05). After adjustment for matching and confounding variables, polyhydramnios was found to be a risk factor for cesarean section (OR 21.02; CI 95% 8.004-55.215, P<0.01).

CONCLUSION: Idiopathic polyhydramnios increased the risk of prolonged first stage of labour, non-vertex presentation and cesarean section.