Impact of ovarian stimulation duration in GnRH antagonist protocols on the cumulative ongoing pregnancy rate in women with normal ovarian reserve: a cohort study

BACKGROUND: The optimal duration of ovarian stimulation in GnRH antagonist protocols remains insufficiently explored, despite its potential impact on oocyte quality, embryo development, and endometrial receptivity. Identifying an optimal stimulation window may improve success rates in assisted reproductive technologies (ART) while minimizing unnecessary hormonal exposure. The aim of the study was to evaluate if the duration of ovarian stimulation in GnRH antagonist IVF/ICSI protocols influence cumulative ongoing pregnancy rates (COPR). METHODS: This retrospective single-centre study analyzed 1456 IVF/ICSI cycles conducted between 2019 and 2023 in women with normal ovarian reserve using an antagonist protocol. Stimulation duration was classified into three categories: ≤ 8 days, 9-13 days (reference), and ≥ 14 days corresponding to the ≤ 5th, 5th-95th, and ≥ 95th percentiles, respectively. Clinical, biological, and embryological outcomes were compared across groups using the Kruskal-Wallis test. Logistic regression was applied to identify independent predictors of cumulative ongoing pregnancy and pregnancy outcomes. RESULTS: A total of 1456 cycles were included in the study. At least one embryo was obtained in 95.2% of cycles, with 69.5% proceeding to fresh transfer. Cumulative ongoing pregnancy was assessed for 1339 cycles, among which 36.4% resulted in an ongoing pregnancy. Stimulation duration did not significantly influence COPR: ≤ 8 days (OR = 1.04, 95% CI 0.78-1.39), 9-13 days (reference), ≥ 14 days (OR = 0.84, 95% CI 0.64-1.11). Multivariate analysis identified younger age and higher AMH as independent predictors of COPR. CONCLUSIONS: In women with normal ovarian reserve undergoing IVF/ICSI with a GnRH antagonist protocol, the duration of ovarian stimulation does not significantly impact cumulative pregnancy outcomes. These findings support a personalized approach to trigger timing based on ovarian response independent of stimulation length.