Case presentation: A 34-year-old Caucasian woman presented to our center with mild vaginal bleeding. Our
patient was 16 weeks pregnant after a seven-year period of primary infertility. She became pregnant following a
non-prescribed regimen of clomiphene citrate extending from the second day to the 13th day of her last cycle. A
transabdominal ultrasound examination revealed a twin pregnancy with complete hydatidiform mole and a
coexisting fetus. Serum b human chorionic gonadotropin was falsely low as identified by serial dilution of the
sample (the ‘hook effect’). Our patient refused termination of pregnancy and she was hospitalized for strict
observation and follow-up. Unfortunately, she developed an attack of severe vaginal bleeding and a hysterotomy
was performed. The fetus died shortly after birth.