Successful pregnancies from the transfer of pronucleate embryos in an outpatient in vitro fertilization program.

Twenty-nine infertile women were given clomiphene citrate (100 mg/day, days 3 to 7), human menopausal gonadotropin (150 IU/day, days 7 to 12 or 13), and human chorionic gonadotropin (2000 IU) for the induction of ovulation. Eggs were collected by laparoscopy and preincubated for 6 hours before being cultured with spermatozoa for fertilization. Approximately 16 to 18 hours after insemination, the eggs that showed two pronuclei were transferred to the patient's uterus. As confirmed by the ultrasonic appearance of a gestational sac, six women who received pronucleate embryos became pregnant, and three pregnancies resulted in normal full-term deliveries. These results confirm that, unlike requirements for most laboratory and farm animals, the requirements of synchrony between the preimplantation human uterus and developing embryos are not very stringent. In vitro fertilization treatment procedures can thus be made simpler by the transfer of embryos at the pronucleate stage.