What it measures.
Follicle-Stimulating Hormone (FSH) is a pituitary glycoprotein that drives folliculogenesis in women and spermatogenesis in men. An elevated Day 3 FSH (>10-12 mIU/mL) signals diminished ovarian reserve — the pituitary is working harder because the ovaries respond less. In men, elevated FSH above 7-12 mIU/mL indicates primary spermatogenic failure.
FSH released from the anterior pituitary in GnRH-driven pulses. In women, it stimulates ovarian follicular development and estrogen production. When ovarian reserve declines, inhibin B and AMH fall, and FSH rises. In men, FSH acts on Sertoli cells to maintain spermatogenesis.
Why it matters.
Day 3 FSH is the classic ovarian reserve test — elevated values predict poor IVF response and diminished fertility potential. In men, FSH level is critical for distinguishing primary testicular failure from secondary (pituitary) causes. The FSH-LH pair determines the treatment pathway in hypogonadism.
Physiology.
FSH is released by the anterior pituitary under GnRH control. In women, it recruits a cohort of follicles each cycle; the dominant follicle produces estradiol and inhibin B which suppress FSH (negative feedback). As the follicle pool shrinks with age, less inhibin B is produced, so FSH rises. In men, FSH stimulates Sertoli cells which support developing sperm and produce inhibin B.
Testing & preparation.
How to prepare
- Women: MUST be drawn on cycle days 2-5 (Day 3 ideal)
- Always draw with estradiol — elevated E2 can mask high FSH
- Men: no timing constraints, draw any day
- Morning draw preferred for consistency
When to test
Women: as part of fertility evaluation, pre-IVF, or when periods become irregular. Men: when semen analysis is abnormal or hypogonadism is suspected.
How often
Each new treatment cycle for women. Annually if monitoring reserve. Men: repeat if initially abnormal, after treatment.
Interpretation.
High follicle-stimulating hormone
Common causes:
- Diminished ovarian reserve (women)
- Perimenopause or menopause (women; FSH >30-40 mIU/mL)
- Primary ovarian insufficiency (women under 40)
- Primary testicular failure (men; Klinefelter, chemotherapy, varicocele)
- Gonadal damage from radiation or surgery
Implications:
- Women: poor IVF prognosis, expedited fertility planning needed
- Men: FSH >7.5 mIU/mL = 5-13x increased odds of abnormal semen
- Men: FSH >12 mIU/mL with small testes = primary testicular failure
- Both: indicates the gonads are not producing adequate sex steroids
Low follicle-stimulating hormone
Common causes:
- Secondary (central) hypogonadism — pituitary or hypothalamic problem
- Hyperprolactinaemia suppressing GnRH
- Exogenous testosterone or anabolic steroids (men)
- Hypothalamic amenorrhoea (women — stress, low BMI, excessive exercise)
- PCOS (FSH is typically low-normal with disproportionately elevated LH)
Implications:
- Investigate pituitary function and prolactin
- In men: potentially treatable with gonadotropin therapy
- In women: evaluate for hypothalamic cause
Optimization.
Diet
- No specific foods lower elevated FSH
- Overall metabolic health supports reproductive axis function
- Adequate caloric intake — caloric restriction elevates FSH context in hypothalamic amenorrhoea
Lifestyle
- Elevated FSH reflects ovarian reserve — not directly modifiable by lifestyle
- Address underlying causes: weight restoration for hypothalamic amenorrhoea
- Stress management supports GnRH pulsatility
Supplements
- No supplements proven to meaningfully lower pathologically elevated FSH
- DHEA studied in poor IVF responders (evidence mixed)
FAQs.
Why must FSH be drawn on Day 3?
Day 3 represents the early follicular baseline when FSH is at its natural recruitment peak. Mid-cycle or luteal phase FSH values cannot be compared to reserve reference ranges and will be misleading.
My FSH is elevated but my AMH is normal — what does that mean?
FSH can vary cycle to cycle while AMH is more stable. An elevated FSH with normal AMH may reflect a 'bad month' or early reserve decline. The combination of AMH + FSH + AFC on ultrasound gives the most complete picture.
Can elevated FSH be treated?
In women, elevated FSH from diminished reserve is a signal, not the problem — lowering FSH doesn't restore eggs. The clinical response is expedited fertility planning. In men with low FSH causing fertility issues, FSH injections (gonadotropin therapy) can stimulate spermatogenesis.