FSH Female
Follicle-stimulating hormone (FSH) tells you what the pituitary is doing to compensate for ovarian aging. As the ovarian follicle pool declines, the negative feedback from inhibin B and estradiol weakens, and the pituitary releases progressively more FSH to recruit each cycle's dominant follicle. A day-3 FSH above 10 IU/L suggests diminished ovarian reserve; above 25 IU/L typically marks perimenopause; sustained values above 40 IU/L are consistent with the postmenopausal range.
Why this biomarker matters
Day-3 FSH is the oldest and most widely used ovarian-reserve marker, predating AMH by decades. It is less sensitive in the early stages of ovarian decline than AMH but remains useful because it integrates pituitary feedback, not just follicle count. A single elevated value is unreliable, FSH varies cycle to cycle by 20–40 percent in perimenopause, so confirm any abnormal result with a repeat measurement and pair with AMH plus antral follicle count on transvaginal ultrasound. In observational cohorts, day-3 FSH above 10 predicts poor response to IVF stimulation and lower live-birth rates per cycle. The transition from cycles where FSH is consistently under 10 to cycles where FSH bounces above 15 typically marks the start of the late reproductive stage. FSH above 25 with at least three months of cycle irregularity is one of the STRAW+10 criteria for late perimenopause. The clinical use is to time fertility decisions and to anchor hormone-therapy discussions around objective data, not symptoms alone.
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