Ultra-Long GnRH-a Pretreatment for FET Outcomes in Patients With Deep Infiltrating Endometriosis

Deep infiltrating endometriosis is a severe form of endometriosis that may reduce fertility and negatively affect pregnancy outcomes after assisted reproductive treatment. Gonadotropin-releasing hormone agonist pretreatment may suppress endometriotic lesions, reduce inflammation, and improve endometrial receptivity, but its benefit before frozen-thawed embryo transfer remains uncertain. This randomized controlled study will evaluate whether ultra-long GnRH-a pretreatment before hormone replacement therapy improves clinical pregnancy outcomes in patients with deep infiltrating endometriosis undergoing their first frozen-thawed embryo transfer cycle. Eligible participants will be randomly assigned to either the GnRH-a pretreatment group or the control group. Participants in the GnRH-a group will receive two injections of long-acting GnRH-a before hormone replacement therapy for endometrial preparation, while participants in the control group will receive routine hormone replacement therapy alone. The primary outcome is clinical pregnancy rate, defined as the presence of a gestational sac on transvaginal ultrasound 30 ± 3 days after embryo transfer. Secondary outcomes include implantation rate, ectopic pregnancy rate, early spontaneous abortion rate, ongoing pregnancy rate at 12 weeks of gestation, and delivery rate. Safety will be evaluated by recording adverse events after GnRH-a injection. The planned enrollment is 120 participants.