The goal of this clinical trial is to learn whether the sudden administration of vaginal micronized progesterone during the late follicular phase can trigger an LH surge and reactivation of oocyte meiosis in healthy oocyte donors aged 18 to 33 undergoing a mild ovarian stimulation cycle. The main question it aims to answer is: * Does progesterone administered in the late follicular phase induce an LH surge and subsequent oocyte meiosis reactivation? Participants will: * Undergo a mild ovarian stimulation with 75 IU of follitropn alfa * Start vaginal micronized progesterone (400 mg every 12 hours) once at least one follicle reaches 15 mm * Have blood samples collected to measure hormone levels before and after progesterone administration * Undergo oocyte retrieval 35-36 hours after the progesterone trigger This is a low-intervention, single-center pilot study including approximately 10 oocyte donors.
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Number of mature oocytes
Timeframe: 35-36 hours after progesterone initiation