Intervention: We propose a protocol for endometrial preparation for frozen/thawed embryo transfer which combines the advantages of both protocols. Patients do not receive estradiol and therefore ovarian follicle production is not suppressed. Progesterone supplementation commences once the endometrium is at least 7 mm, a follicle is demonstrated on TVS, and ovulation has not yet taken place. The day of ET is scheduled according to the unit's working days and progesterone suppositories are commenced 48 hours before the scheduled embryo transfer. In order to ensure synchronization between the endometrium and the embryos, embryo transfer of 48 hour embryos will be transferred 48 hours after progesterone therapy. This is not different from our current practice.