This randomized clinical trial aims to assess the comparative effectiveness of two distinct endometrial preparation protocols for frozen embryo transfer (FET) among women with adenomyosis undergoing IVF/ICSI. Specifically, it seeks to address the following key questions: 1. Does the protocol involving the combination of GnRH agonist and letrozole for down regulation with exogenous steroids (GnRHa+AI - AC) result in a higher live birth rate compared to the use of exogenous steroids alone (AC) in women with adenomyosis undergoing frozen embryo transfer? 2. What are the common side effects of the GnRHa+AI - AC regimen? Eligible participants will undergo screening before endometrial preparation for FET, following which they will be randomly assigned to one of two groups: GnRHa+AI - AC or AC. In the GnRHa+AI - AC group, participants will be pre-treated with GnRH agonist and letrozole two months before endometrial preparation. After this period, participants will return for endometrial preparation, and any side effects resulting from the down regulation will be evaluated. In contrast, the AC group will receive standard treatment.