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

Deep infiltrating endometriosis is a severe subtype of endometriosis that may involve pelvic organs and is associated with infertility, impaired endometrial receptivity, chronic pelvic inflammation, reduced implantation, increased miscarriage risk, and poorer outcomes after assisted reproductive treatment. For patients with deep infiltrating endometriosis who require frozen-thawed embryo transfer, the optimal endometrial preparation strategy remains uncertain. Gonadotropin-releasing hormone agonists may suppress ovarian estrogen production, inhibit the activity of endometriotic lesions, reduce inflammatory mediators, and potentially improve the endometrial environment before embryo transfer. However, current evidence regarding GnRH-a pretreatment before frozen-thawed embryo transfer in patients with endometriosis is inconsistent, and high-quality prospective randomized controlled studies are limited. This study is designed to evaluate whether ultra-long GnRH-a pretreatment improves pregnancy outcomes in patients with deep infiltrating endometriosis undergoing frozen-thawed embryo transfer. This is a prospective, randomized, controlled, single-center clinical study. A total of 120 eligible participants will be enrolled. Participants must be younger than 40 years, diagnosed with deep infiltrating endometriosis by ultrasound at the study center, undergoing their first frozen-thawed embryo transfer cycle with hormone replacement therapy for endometrial preparation, and have at least one good-quality frozen embryo. Eligible participants will be randomly assigned in a 1:1 ratio to the experimental group or the control group. Participants in the experimental group will receive ultra-long GnRH-a pretreatment before frozen-thawed embryo transfer. Long-acting GnRH-a will be administered on menstrual cycle days 2 to 4, followed by a second injection 28 to 30 days later. Hormone replacement therapy for endometrial preparation will begin 28 to 30 days after the second GnRH-a injection, followed by frozen-thawed embryo transfer according to routine clinical practice. Participants in the control group will undergo routine hormone replacement therapy for endometrial preparation before frozen-thawed embryo transfer without GnRH-a pretreatment. The primary outcome is clinical pregnancy rate, defined as the presence of a gestational sac detected by 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. Additional pregnancy, obstetric, and neonatal outcomes may be followed according to the study protocol, including biochemical pregnancy, late spontaneous abortion, preterm birth, stillbirth, live birth, pregnancy complications, delivery outcomes, and birth weight. Safety will be assessed by monitoring and recording adverse events after GnRH-a injection, including hot flashes, headache, sleep disturbance, vaginal bleeding or spotting, night sweats, and mood changes. Participants will be followed after embryo transfer and, if pregnancy occurs, through pregnancy and delivery according to the protocol-defined follow-up schedule.