Follicle-Stimulating Hormone (FSH)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 13, 2026

Follicle-Stimulating Hormone (FSH) is a glycoprotein gonadotropin secreted by the anterior pituitary gland in response to hypothalamic GnRH pulses, with the primary function of stimulating ovarian follicle recruitment and maturation during the follicular phase of the cycle. Each cycle, FSH recruits a cohort of follicles. One typically becomes dominant and proceeds to ovulation. That process depends on an FSH rise that begins in the late luteal phase of the prior cycle, well before menstruation starts.

Basal FSH, drawn on cycle day 2, 3, or 4, is a standard component of an ovarian reserve panel. An elevated basal FSH signals that the pituitary is working harder than normal to recruit follicles. This reflects reduced ovarian sensitivity, often an early indicator of declining reserve. The threshold for "elevated" varies by laboratory and by age, and a single elevated value carries less weight than a persistently rising trend across multiple cycles.

FSH must be read alongside AMH, AFC, and estradiol drawn on the same day. Estradiol elevated on day 3 can suppress FSH artificially, masking the true reserve picture. A normal FSH with elevated estradiol is not reassuring. The panel is only interpretable together.

A large study of women 30 to 44 years old found that elevated FSH was independently associated with infertility across all age groups, confirming its relevance beyond the IVF context where it is most commonly discussed.¹

In men, FSH stimulates Sertoli cells and supports spermatogenesis. Elevated FSH in a man with low sperm counts often signals primary testicular failure. That finding changes the clinical approach entirely and is part of why male factor evaluation belongs at the first visit, not as an afterthought.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.