Late-Start Corifollitropin Alfa in Mild Ovarian Stimulation

This prospective randomized clinical study evaluates a novel physiology-oriented mild ovarian stimulation protocol based on the delayed initiation of corifollitropin alfa. Unlike conventional ovarian stimulation, which begins during the early follicular phase, the proposed protocol postpones exogenous gonadotropin administration until cycle day 4, allowing physiological follicular recruitment to occur before ovarian stimulation. Participants are randomly assigned to one of two strategies for prevention of premature luteinizing hormone (LH) surge: daily GnRH antagonist administration, or progesterone-primed ovarian stimulation (PPOS). The primary objective is to evaluate ovarian response and the feasibility of this simplified stimulation strategy. Secondary objectives include embryological outcomes, pregnancy outcomes, gonadotropin consumption, treatment burden, and the proportion of patients completing stimulation without supplementary gonadotropin administration. The study aims to determine whether a physiology-oriented late-start stimulation protocol can simplify IVF treatment while maintaining satisfactory embryological and clinical outcomes.

Inclusion Criteria: * Female participants aged 28 to 43 years at the time of enrollment. * Clinical diagnosis of infertility requiring IVF or ICSI treatment. * Planned controlled ovarian stimulation according to the study protocol. * Anti-Müllerian hormone concentration of 0.2 ng/mL or greater. * Presence of both ovaries. * Ability to provide written informed consent. * Willingness to comply with all study procedures and follow-up assessments. Exclusion Criteria: * Age younger than 28 years or older than 43 years. * Anti-Müllerian hormone concentration below 0.2 ng/mL. * Untreated endocrine disorders that may interfere with ovarian stimulation, including uncontrolled thyroid disease or hyperprolactinemia. * Contraindication to ovarian stimulation, pregnancy, or transvaginal oocyte retrieval. * Severe systemic disease considered by the investigator to make participation unsafe. * Concurrent participation in another interventional clinical study that could interfere with the study outcomes. * Refusal or inability to provide written informed consent. * Previous enrollment in this study.