Hydramnios: anomaly prevalence and sonographic detection

To characterize the prevalence and ultrasound detection of fetal anomalies in pregnancies with hydramnios, and to estimate anomaly and aneuploidy risks when no sonographic abnormality is noted.

This was a retrospective cohort study of singleton pregnancies with hydramnios. Hydramnios was categorized as mild, moderate, or severe based on greatest amniotic fluid index of 25.0-29.9 cm, 30.0-34.9 cm, or 35.0 cm or more, respectively. Antenatal anomaly detection was compared with assessment in the immediate neonatal period. Aneuploidy and fetal deaths were analyzed separately.

Hydramnios was diagnosed in 672 pregnancies, and 77 (11%) of neonates had one or more anomalies. Though more severe hydramnios was associated with higher likelihood of anomaly (P <.001), sonographic anomaly detection (79%) did not differ according to degree of hydramnios (P =.4). Of anomalies which eluded sonographic diagnosis, cardiac septal defects, cleft palate, imperforate anus, and tracheoesophageal fistula were the most frequent. If sonographic evaluation was normal, the risk of a major anomaly was 1% with mild hydramnios, 2% with moderate hydramnios, and 11% with severe hydramnios (P <.001). Aneuploidy was present in 10% of fetuses with sonographic anomalies and 1% without apparent sonographic anomalies. The fetal death rate was 4% in the setting of hydramnios; 60% of these cases had anomalies.

The anomaly detection rate in pregnancies with hydramnios was nearly 80%, irrespective of the degree of amniotic fluid increase. Residual anomaly risk after normal sonographic evaluation was 2% or less if hydramnios was mild or moderate and 11% if severe.