Ovulation is not essential for embryo implantation in the endometrial lining as demonstrated in the hormone replacement protocol. In the proposed protocol the developing follicle stimulates endometrial growth and progesterone is commenced once endometrial growth reaches at least 7 mm and the dominant follicle has been established, regardless of when ovulation occurs. Embryo transfer is performed 48 hours after beginning progesterone. By dissociating the protocol from the day of ovulation greater leeway is achieved in choosing the day of embryo transfer.