Sonographic features of the triploid fetus.

The sonographic characteristics of six viable triploid fetuses, with gestational ages ranging from 16 to 33 weeks, are presented. Each pregnancy was associated with decreased amniotic fluid volume, a significant lag in biparietal diameter and femur length, and severe head-to-body disproportion. No placental abnormalities were noted on ultrasound and only one placenta demonstrated hydropic change (15% to 20% of villi) on pathologic examination. Since the nonmolar triploid fetus often presents with unexplained intrauterine growth retardation, identification of its characteristic sonographic features allows for karyotype confirmation and the avoidance of inappropriate obstetric management.