Ultrasound diagnosis of coexisting molar pregnancy following referral for abnormal serum screen

Complete hydatidiform mole and coexistent fetus is a rare occurrence. We report a case of a patient referred for abnormal serum screen and vaginal bleeding in the second trimester of pregnancy. Ultrasound revealed a cystic and solid mass along the posterior uterine wall with multiple hypoechoic (honeycomb) areas noted, consistent with molar degeneration of the placenta. Separate from this mass was a coexisting viable fetus with normal fetal anatomy and distinct anterior placenta. At delivery, a large cystic mass of placenta! tissue appeared to be implanted separately from a normal-appearing fetus and placenta. The mass weighed 184 g and contained multiple 1- to 1.5-cm cysts throughout. Microscopic sections revealed hydropic chorionic villi with central cistern formation and nonpolar trophoblastic hyperplasia with atypia, compatible with complete hydatidiform mole. This case illustrates that the diagnosis of coexisting molar pregnancy after referral for abnormal serum screen should be considered, especially if maternal serum β-human chorionic gonadotropin is high and the patient has vaginal bleeding.