The authors have performed selective birth in two twin pregnancies in the same patient. The couple's first pregnancy resulted in the birth of a male with Tay Sachs disease: their Pergonal-induced second pregnancy was a twin gestation discordant for Tay Sachs disease. A fetal intracardiac puncture, exsanguination, and fetal intracardiac air embolization were then performed. The patient went into premature labor 9 days later and delivered a normal immature infant, who died, and the macerated cotwin. The third Pergonal-induced pregnancy was a singleton with Tay Sachs disease and the pregnancy was terminated. Their fourth Pergonal-induced pregnancy was a twin gestation discordant for Tay Sachs disease. At 20 weeks gestation, fetal intracardiac air embolization was performed with immediate demise of the affected fetus. The pregnancy was followed closely with ultrasonography and coagulation studies and proceeded to term without complication. A normal female and a fetus papyraceous were delivered by cesarean section.