FSH (Follicle-Stimulating Hormone)
FSH is released by the anterior pituitary and stimulates ovarian follicle development and estradiol production in women, and spermatogenesis in men. FSH feedback is essential for reproductive function. In women, FSH peaks at mid-cycle and varies with cycle phase; in men it is relatively stable. Day 2–3 FSH is the traditional marker of ovarian reserve (though AMH has largely taken that role). Elevated FSH in women is the hallmark of menopause or premature ovarian insufficiency.
Reference Ranges
Male
1.5 – 12.4
mIU/mL
Female
3.5 – 12.5
mIU/mL
Child
Consult pediatrician
Reference ranges may vary by laboratory. Always compare with the range printed on your lab report.
What Low Levels Mean
Low FSH with low estradiol in a woman with amenorrhea suggests hypothalamic or pituitary dysfunction — causes include stress, weight loss, over-exercise, hyperprolactinemia, and pituitary adenoma. In men, low FSH with low testosterone suggests secondary (central) hypogonadism and warrants pituitary imaging. Oral contraceptives also suppress FSH.
What High Levels Mean
In women, elevated FSH — especially on day 2–3 of the cycle — suggests diminishing ovarian reserve. FSH above 25 mIU/mL with amenorrhea confirms menopause or premature ovarian insufficiency. In men, elevated FSH with low testosterone suggests primary (testicular) hypogonadism — causes include Klinefelter syndrome, prior chemotherapy or radiation, cryptorchidism, varicocele, testicular trauma.
Frequently Asked Questions
Why is day 2–3 FSH measured for ovarian reserve?
Early follicular-phase FSH correlates with how hard the pituitary is working to stimulate the ovary — higher FSH suggests reduced ovarian responsiveness. However, FSH varies month to month, and a single normal value does not rule out poor ovarian reserve. AMH (anti-Müllerian hormone) is more stable across the cycle and has largely replaced day-3 FSH as the primary reserve marker in IVF clinics.
What does FSH tell us about menopause?
Sustained FSH above 25 mIU/mL with amenorrhea for 12 months confirms menopause. Perimenopausal women may have fluctuating FSH, so a single value can be misleading. Symptoms (hot flashes, night sweats, sleep disturbance, mood changes, vaginal dryness) are often more useful than lab testing to guide management.
Should men with low libido get FSH tested?
Yes — along with LH, testosterone, SHBG, and prolactin. This panel distinguishes primary (testicular, high FSH/LH) from secondary (central, low FSH/LH) hypogonadism. The cause shapes treatment: primary needs testosterone replacement; secondary may need replacement or gonadotropin therapy depending on fertility goals.
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nmol/LThis information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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