What this test measures
Follicle Stimulating Hormone (FSH) is a gonadotropin secreted by the anterior pituitary in response to hypothalamic GnRH. In women, FSH recruits ovarian follicles and supports their growth in the first half of the menstrual cycle. In men, FSH supports Sertoli cell function and spermatogenesis.
FSH levels are tightly regulated by negative feedback from gonadal sex steroids (estradiol, testosterone) and inhibin B. The assay measures total serum FSH in mIU/mL.
Why it matters
FSH is one of the most informative single hormones in reproductive medicine. In women, an early-follicular FSH (day 2/3 of cycle) is used in fertility workup; a raised FSH (> 10 mIU/mL) suggests diminished ovarian reserve, while a very high FSH (> 25) with absent periods confirms premature ovarian insufficiency or menopause. A normal early-follicular FSH does not guarantee good fertility — AMH and antral follicle count are now considered equally or more informative.
In men, FSH is part of the hypogonadism workup alongside LH and testosterone. A raised FSH with low testosterone = primary testicular failure; low FSH with low testosterone = secondary (pituitary or hypothalamic) hypogonadism. In adolescents, FSH/LH help characterise delayed or precocious puberty. In a child with cryptorchidism or known Klinefelter syndrome, persistently raised FSH after puberty indicates established testicular failure.
How to prepare
No fasting required. Best done morning. In cycling women, draw on cycle day 2 or 3 for fertility workup. Stop biotin for 48–72 hours. Tell the lab if you are on hormonal contraception, HRT or fertility medications.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Follicle Stimulating Hormone (mIU/mL)[1][2] | Female follicular: 3.5 – 12.5 · Mid-cycle peak: 4.7 – 21.5 · Luteal: 1.7 – 7.7 · Postmenopausal: 25.8 – 134.8 · Adult male: 1.5 – 12.4 | Low FSH with low LH and low sex steroids = hypogonadotropic hypogonadism — pituitary or hypothalamic problem (tumour, functional hypothalamic amenorrhoea from low BMI / over-exercise / stress, Kallmann syndrome). May also be seen with combined oral contraceptive use. | Raised FSH in a woman with a raised LH and absent periods suggests primary ovarian failure. Early-follicular FSH > 10 mIU/mL in a younger woman flags diminished ovarian reserve. In a man, a raised FSH with low testosterone indicates primary testicular failure (Klinefelter, post-orchitis, post-chemotherapy, varicocele-related testicular damage). |
FSH — interpretation by scenario
| Scenario | FSH | LH | Sex steroid | Likely picture |
|---|---|---|---|---|
| Reproductive-age woman, fertile | < 10 (day 2/3) | < 10 | Normal | Normal |
| Diminished ovarian reserve | 10 – 25 | Normal | Normal/low | Reserve declining |
| Premature ovarian insufficiency / menopause | > 25 | High | Low E2 | Ovarian failure |
| Hypothalamic amenorrhoea | Low | Low | Low E2 | Stress / low BMI / over-exercise |
| PCOS | Normal/low | High | Normal | LH:FSH > 2 |
| Primary testicular failure (M) | High | High | Low T | Klinefelter, post-chemo, orchitis |
| Secondary hypogonadism (M) | Low | Low | Low T | Pituitary disease |
Frequently asked questions
When in my cycle should FSH be tested?
For fertility workup, cycle day 2 or 3 (counting day 1 as the first day of full flow). FSH varies through the cycle and a non-baseline sample is hard to interpret.
My FSH is 15 — am I in menopause?
Not necessarily. An FSH of 15–25 in a perimenopausal woman with irregular periods suggests declining ovarian reserve. Postmenopausal FSH is usually above 30 with absent periods for 12 months. Repeat testing and the clinical picture matter.
I have PCOS — what does FSH look like?
In PCOS, FSH is usually normal or slightly low, while LH is high — giving an LH:FSH ratio above 2, which is one of the supportive biochemical markers (not on its own diagnostic).
I am a man and my FSH is high — what does that mean?
A raised FSH with low testosterone in a man indicates that the testes are failing — common causes include Klinefelter syndrome, past orchitis (mumps), post-chemotherapy damage, or significant varicocele. Further workup includes LH, total testosterone, semen analysis and karyotype.
Do contraceptive pills affect FSH?
Yes — combined oral contraceptives suppress FSH. Test 3 months after stopping for a true baseline.
Is FSH still useful given that AMH is now available?
Yes. FSH and AMH measure different things — AMH reflects the resting follicle pool, FSH reflects how hard the pituitary is having to work to recruit. They are complementary, and most fertility clinics use both.
Can a single high FSH confirm menopause?
Not on its own — postmenopausal FSH is usually consistently > 30 with absent periods for 12 months. A single value can be misleading in perimenopause where FSH fluctuates wildly cycle to cycle.
Related Hormones / Endocrine tests
Tests commonly ordered alongside FOLLICLE STIMULATING HORMONE (FSH), or that help interpret an unexpected result.
Sources & references
- Endocrine Society — Female Infertility · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — FSH Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Follicle Stimulating Hormone · accessed 2026-05-30T00:00:00.000Z
- ASRM — Diagnostic Evaluation of the Infertile Female · accessed 2026-05-30T00:00:00.000Z
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