GnRH Agonist Pretreatment Duration and Letrozole Supplementation in Frozen Embryo Transfer for Adenomyosis Patients

This randomized clinical trial aims to assess the comparative effectiveness of different pre-treatment protocols prior to frozen embryo transfer (FET) among women with adenomyosis, providing evidence-based guidance for clinical decision-making. The main questions it aims to answer are: Does the protocol involving two doses of gonadotropin-releasing hormone agonist (GnRH-a) pretreatment result in a higher live birth rate compared to one dose of GnRH-a pretreatment in women with adenomyosis undergoing frozen embryo transfer? Does the protocol involving GnRH-a with letrozole supplementation result in a higher live birth rate compared to GnRH-a monotherapy in women with adenomyosis undergoing frozen embryo transfer? Eligible participants will undergo screening before endometrial preparation for FET, following which they will be randomly assigned to one of four groups: GnRH-a-1M, GnRH-a-2M, GnRH-a+LE-1M or GnRH-a+LE-2M. In the GnRH-a-1M group, participants will be pre-treated with one dose GnRH agonist before endometrial preparation. In the GnRH-a-2M group, participants will be pre-treated with two doses GnRH agonist before endometrial preparation. In the GnRH-a+LE-1M group, participants will be pre-treated with one dose GnRH agonist and letrozole 28 days before endometrial preparation. In the GnRH-a+LE-2M group, participants will be pre-treated with two doses GnRH agonist, along with daily 2.5 mg letrozole for 28 days since the first injection of GnRH agonist before endometrial preparation. After pre-treament, all participants will return for endometrial preparation in artificial cycles.