Hydramnios: anomaly prevalence and sonographic detection

OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.