Genetic implications of idiopathic hydramnios.

The antenatal diagnosis of hydramnios requires a careful search for associated underlying maternal or fetal conditions. Even in pregnancies associated with idiopathic hydramnios in which no underlying condition can be identified, a high perinatal mortality rate exists. Although trisomy 18 has been seen in pregnancies with hydramnios and growth retardation, the association with specific chromosomal disorders and idiopathic hydramnios has not been well defined. A review of pregnancies complicated by hydramnios was undertaken; 99 cases with complete pregnancy and delivery information were identified. Fifty-nine pregnancies were complicated by idiopathic hydramnios, and except for the hydramnios, sonographic evaluation was normal. Delivery information revealed one infant with trisomy 18 and eight infants with structural anomalies not appreciated antenatally. Of the undiagnosed malformations, 25% are frequently associated with trisomy 21. We recommend fetal chromosomal analysis as an adjunct to the evaluation of pregnancies complicated by idiopathic hydramnios.