FSH (Follicle-Stimulating Hormone)

What is FSH

FSH (Follicle-Stimulating Hormone) is a hormone produced by the pituitary gland that regulates the reproductive system. In women, FSH stimulates the maturation of follicles (the "capsules" containing eggs) in the ovaries. In men, FSH stimulates spermatogenesis (sperm production) in the testes.

FSH and LH act as a pair: the pituitary gland regulates both through a feedback mechanism involving sex hormones (estradiol, testosterone, inhibin). For this reason, both are usually tested together.

Reference ranges

Men: 1.5–12.4 IU/L.

Women — depends on the phase of the menstrual cycle:

• Follicular phase: ~3–10 IU/L
• Ovulation peak: ~6–25 IU/L
• Luteal phase: ~1–9 IU/L
• Menopause: ~25–135 IU/L

The laboratory's reference range is the most important — it reflects the method and calibration used.

Why FSH may be elevated

• Menopause — the ovaries no longer respond to pituitary signals, so FSH rises compensatorily. FSH >25–30 IU/L often indicates menopausal status.
• Primary ovarian insufficiency (POI) — persistently elevated FSH in young women may indicate early loss of ovarian function.
• Testicular insufficiency (men) — elevated FSH following trauma, infection, or other causes indicates impaired spermatogenesis.
• Klinefelter syndrome — a genetic condition in men in which FSH is typically elevated.
• Diminished ovarian reserve — elevated FSH in the early follicular phase (cycle day 3) may indicate declining ovarian reserve.

Why FSH may be low

• Hypothalamic or pituitary disorders — a central cause that suppresses FSH production.
• Stress and poor nutrition — chronic stress, anorexia, or sudden weight loss can suppress the hypothalamic-pituitary axis.
• Hormonal contraception — suppresses FSH to prevent ovulation.
• Hyperprolactinemia — elevated prolactin suppresses gonadotropin (FSH and LH) secretion.
• Anabolic steroid use — exogenous androgens suppress FSH production in men.
• Pregnancy — FSH is physiologically suppressed.

Next steps

FSH results must always be interpreted alongside other hormones and clinical data. A single elevated or low FSH result is not a diagnosis.

Your doctor may recommend:

• For women — repeat FSH on cycle day 3 (the standard assessment time).
• Testing AMH (anti-Müllerian hormone) to assess ovarian reserve.
• Testing estradiol, LH, prolactin, and progesterone.
• For men — testing testosterone and performing a semen analysis.

Monitoring over time

FSH trends are particularly informative in the context of fertility. For women planning pregnancy, monitoring FSH over several cycles shows the trajectory of ovarian reserve. During perimenopause, rising FSH confirms an approaching menopause.

For men being evaluated for fertility, assessing FSH stability helps determine whether the problem is central (at the pituitary level) or peripheral (at the testicular level).

Questions for your doctor

1. Does my FSH level match my cycle phase and age? 2. What does the ratio of my FSH to LH indicate? 3. Should I have AMH tested to assess my ovarian reserve? 4. Does my FSH suggest approaching menopause or early ovarian insufficiency? 5. Should the test be repeated on a specific cycle day for a more accurate result?

*This is not medical advice. Consult your doctor regarding any health-related decisions.*