Idiopathic polyhydramnios and postnatal abnormalities.

OBJECTIVE To investigate the proportion and type of fetal anomalies that are associated with polyhydramnios and to examine whether in cases with idiopathic polyhydramnios during the course of pregnancy and fetal anomalies only diagnosed after birth, antenatal characteristics differ. METHODS This was a retrospective study involving all pregnancies with polyhydramnios defined by a deepest pool of amniotic fluid ≥8 cm and a detailed ultrasound examination, a 75 g glucose tolerance test and a TORCH serology. RESULTS Between 2004 and 2010, 272 pregnancies fulfilled the inclusion criteria. In 89 (32.7%) and 65 (23.9%) cases, there was a fetal anomaly or diabetes. In 118 (43.4%) pregnancies, polyhydramnios was classified as idiopathic. In 11 (9.3%) of the 118 fetuses, an anomaly was found after birth, mainly gastrointestinal atresia. In these cases, median deepest pool of amniotic fluid was 9.6 cm, and median estimated fetal weight was at the 69th centile, whereas in cases without anomalies diagnosed after birth, median deepest pool was 9.0 cm and median estimated fetal weight at the 90th centile (Mann-Whitney U test: deepest pool p = 0.116, and estimated fetal weight centile p = 0.377). There was also no difference in the maternal and gestational age distribution of these cases (Mann-Whitney U test: maternal age p = 0.293, and gestational age p = 0.499). CONCLUSION In about 40% of pregnancies, polyhydramnios remains unexplained during the course of pregnancy. In 10% of these cases, an anomaly will only be found after birth. In this group, antenatal characteristics such as amniotic fluid volume, estimated fetal weight or gestational and maternal age at the time of diagnosis do not help to detect these anomalies before birth.