FSH, follitropin
HormonesAlso known as: follicle stimulating hormone, follicle-stimulating hormone, follitropin
FSH (Follicle Stimulating Hormone) is a pituitary hormone that stimulates egg development in ovaries and sperm production in testes.
FSH levels vary throughout the menstrual cycle, surge during ovulation, and rise drastically after menopause when ovaries stop responding.
Why this matters
FSH levels reflect reproductive system activity and overall hormonal balance. Abnormally high or low levels can indicate changes in fertility, menopausal status, or pituitary function.
How this connects to other biomarkers
- In men, elevated FSH with low Testosteron, total indicates the testicles themselves are failing (primary testicular failure); low FSH with low testosterone suggests the brain/pituitary is the problem (secondary hypogonadism).
- In women, persistently elevated FSH (> 25 IU/L) with low estradiol confirms menopause; an LH/FSH Ratio > 2 in pre-menopausal women raises suspicion for PCOS (polycystic ovary syndrome).
- FSH > 40 IU/L in young women with absent periods suggests primary ovarian insufficiency (early menopause).
How often should I test FSH, follitropin?
For premenopausal women, baseline FSH is drawn on day 2 to 5 of the cycle. For postmenopausal women and men, yearly testing alongside other hormones is appropriate. On hormone therapy, retest at 6 to 12 weeks after dose changes.
At baseline / for screening: Once every 12 months from age 35, with cycle phase noted in premenopausal women (typically drawn on day 2 to 5 of a 28-day cycle for baseline). More frequently during perimenopause.
When monitoring an intervention or change: Retest 6 to 12 weeks after starting or adjusting hormone therapy (HRT, oral contraceptives, fertility medication). Cycle phase matters as much as cadence, so match the cycle day across draws for meaningful comparison. In perimenopause, expect significant cycle-to-cycle variability that settles only after menopause is established.
Note: FSH varies less by pulse than LH but still shifts across the cycle. Draw on day 2 to 5 in premenopausal women; during perimenopause, retest every 6 months as rising FSH reflects falling ovarian reserve.
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