Incidence of fetal malformations in pregnancies complicated by oligo- and polyhydramnios

Oligo- and polyhydramnios could be observed in 1%–7% of all pregnancies and are associated with an increased risk of fetal anomalies. We evaluated the fetal outcomes of 840 pregnancies with oligo- and polyhydramnios on the basis of ultrasonographic findings (oligohydramnios: single deepest pocket <2 cm, polyhydramnios: single deepest pocket >8 cm) between 12 and 42 weeks of gestation. We observed 734 pregnancies (752 fetuses) with oligohydramnios and 106 pregnancies (108 fetuses) with polyhydramnios. Of the 752 fetuses with oligohydramnios, 81% survived and 19% died in utero. Among the 108 fetuses of pregnancies with polyhydramnios, 72% of the babies survived and 28% died in utero. In polyhydramnios, 48% (52 of 108) of the fetuses had severe malformations, which is significant compared to the rate of 11.8% (89 of 752) of fetal malformations in oligohydramnios (P-value<0.001). Oligohydramnios is predominantly associated with malformations of the urinary tract, whereas polyhydramnios is associated with anomalies of the gastrointestinal tract. In conclusion, measurement of single deepest pocket is a valuable screening method to evaluate pregnancies showing the complications of oligo- and polyhydramnios. Pregnancies with severe polyhydramnios have a poorer outcome and fetuses have a significantly higher risk of congenital malformations compared to pregnancies with oligohydramnios.