Significance of idiopathic midtrimester polyhydramnios.

It is uncertain whether idiopathic midtrimester polyhydramnios is associated with adverse perinatal outcome. Fifty patients with midtrimester polyhydramnios without apparent etiology were compared to 85 control patients. Demographic, obstetric, and neonatal data were recorded and compared using chi-square, Fisher's exact, and Student t tests. Comparisons were also made within the study group between those patients with resolution of the polyhydramnios and those with persistence. Demographic and obstetric data were similar in both groups. Of study patients, 94% had mild polyhydramnios, which resolved in 75.6% of those having follow-up scans. There were no differences in neonatal outcome between study and control groups. Fetal aneuploidy was increased in the persistent polyhydramnios group (2 of 10, 20%) compared to the group with spontaneous resolution (none of 33, 0%), P = 0.049. Mild idiopathic midtrimester polyhydramnios resolves frequently and, if so, is not associated with adverse perinatal outcome. However, persistence of polyhydramnios is associated with an increased risk of fetal aneuploidy, and fetal karyotyping should be considered.