Follicle-Stimulating Hormone (FSH)

FSH is a glycoprotein hormone secreted by the anterior pituitary gland. It orchestrates key events in the reproductive systems of both sexes.

Function

• Women: Stimulates growth and maturation of ovarian follicles (egg-containing sacs) and regulates the menstrual cycle.

• Men: Promotes spermatogenesis by acting on Sertoli cells within the testes.

Normal Ranges
(measured in mIU/mL and may vary slightly by laboratory)

• Females:

  • Follicular phase: 3.85 – 8.78

  • Midcycle (ovulatory peak): 4.50 – 22.50

  • Luteal phase: 1.80 – 5.00

  • Post-menopause: 16.70 – 114.00

• Males:

  • Ages 1 day– < 13 years: 1.50 – 14.00

  • Age ≥ 13 years: 0.70 – 11.10

Clinical Significance

• Low FSH in Women: Hypothalamic or pituitary dysfunction, ovarian failure, polycystic ovary syndrome (PCOS)

• High FSH in Women: Menopause, primary ovarian insufficiency, ovarian failure

• Low FSH in Men: Testicular dysfunction, pituitary disorders

• High FSH in Men: Testicular failure (e.g., following chemotherapy or in Klinefelter syndrome)

Symptoms of Imbalance

• FSH Deficiency:

  • Women: Irregular or absent periods, anovulation, infertility

  • Men: Low sperm count, reduced libido, infertility

• Excess FSH:

  • Women: Early menopause symptoms (hot flashes, vaginal dryness)

  • Men: May reflect compensatory rise in response to testicular failure; rarely causes overt symptoms

Diagnosis

• Test: Blood sample drawn—timed in women according to cycle phase.

• Interpretation: Correlate with

  • Luteinizing Hormone (LH)

  • Estradiol (in women) or testosterone (in men)

  • Clinical history and physical exam

Frequently Asked Questions

1. What causes low FSH levels?

   • Pituitary or hypothalamic disorders, stress, weight extremes, PCOS.

2. Can FSH levels predict menopause?

   • Rising baseline FSH helps indicate perimenopause; not definitive alone.

3. How does FSH affect fertility?

   • Essential for follicle maturation in women and sperm production in men.

4. What is the relationship between FSH and estrogen?

   • In women, rising estrogen during the follicular phase exerts negative feedback on FSH; the midcycle estrogen peak triggers the LH/FSH surge for ovulation.

5. How is FSH measured?

   • Via a blood test, often drawn on day 3 of the menstrual cycle in women or any time in men.