Double Occupancy.

A 33-year-old woman, pregnant for the first time, presented for obstetric care after in vitro fertilization. Her pregnancy was confirmed when a single intrauterine gestation sac was demonstrated on ultrasound at 5 weeks’ gestation (3 weeks after embryos were transferred). Except for a history of infertility, the patient had no medical problems. A 3-dimensional ultrasound scan, performed at 14 weeks’ gestation, highlighted an additional and unusual risk for complications (Figure 1).