Comparison of different ovarian stimulation protocols on pregnancy outcome in women with endometriosis undergoing frozen embryo transfer

This study aimed to evaluate the efficacy of three distinct controlled ovarian stimulation (COS) protocols—long GnRH-agonist (GnRH-a) protocol, GnRH-antagonist (GnRH-ant) protocol, and mild-ovarian stimulation protocol—in endometriosis patients undergoing frozen embryo transfer therapy. The research involved 636 women with endometriosis during 2015–2022. These patients received different COS protocols, including 118 cases with GnRH-a, 295 with GnRH-ant, 223 with mild‑stimulation protocol. Inverse probability of treatment weighting was used to adjust baseline features to reduce bias. The pregnancy outcomes were evaluated among the groups. In the analysis, the live birth rate was lower in the GnRH-ant group (odds ratio [OR] 0.62, 95% confidence interval [CI] 0.47–0.83, P = 0.001) than in the GnRH-a group with no differences in other key pregnancy outcomes. The mild group showed no difference in live birth rate vs. GnRH-a group, but lower biochemical pregnancy rate (OR 0.73, 95% CI 0.54–0.98, P = 0.04) and high-quality embryo rate (OR 0.69, 95% CI 0.51–0.94, P = 0.02). For patients with stage III–IV endometriosis undergoing FET, mild‑stimulation and GnRH-a protocols are more favorable than GnRH-ant due to higher live birth rates.