Traditionally, the use of GnRH-a suppression was considered essential for adequate endometrial hormonal modulation in cryopreserved-thawed embryo transfer cycles. Several studies, however, have questioned its necessity for controlled endometrial preparation. Using a high dose of estradiol from day 1 of the cycle will suppress the gonadotroph, preventing folliculogenesis and excessive secretion of LH, allowing adequate endometrial preparation without GnRH-a.