Follicle Stimulating Hormone
FSH
Clinical Overview
FSH is a gonadotropin hormone secreted by the anterior pituitary gland. In women, it stimulates ovarian follicle growth and estrogen production. In men, it stimulates Sertoli cells and is essential for spermatogenesis. FSH is critical for evaluating fertility, menstrual irregularities, and menopause.
Why This Test Matters
FSH is a key test in the fertility workup. Elevated FSH in women (especially on cycle day 2–3) indicates diminished ovarian reserve — the pituitary must work harder because fewer follicles remain. A high FSH with absent periods in women under 40 suggests premature ovarian insufficiency (POI). In men, elevated FSH with azoospermia suggests primary testicular failure; low FSH with low testosterone suggests hypogonadotropic hypogonadism (pituitary or hypothalamic cause).
Reference RangesWHO/IFCC standards
| Age Group | Sex | Reference Range | Unit | Notes |
|---|---|---|---|---|
| Adults (18–64) | Female | 3.5 – 12.5 | mIU/mL | Follicular phase (day 2–3 of cycle) |
| Adults (18–64) | Female | 4.7 – 21.5 | mIU/mL | Ovulatory peak |
| Adults (18–64) | Female | 25.8 – 134.8 | mIU/mL | Post-menopause |
| Adults (18–64) | Male | 1.5 – 12.4 | mIU/mL | — |
Also reported in: IU/L.
What Causes Abnormal Results?
High FSH Causes
- Menopause (normal physiological rise)
- Premature ovarian insufficiency (POI) — in women <40
- Primary testicular failure (Klinefelter syndrome, chemotherapy damage)
- Gonadal dysgenesis
- Turner syndrome
- Autoimmune oophoritis
Low FSH Causes
- Hypogonadotropic hypogonadism (pituitary or hypothalamic failure)
- Hyperprolactinemia (prolactin suppresses GnRH and FSH)
- Severe caloric restriction or eating disorders
- Excessive exercise (functional hypothalamic amenorrhea)
- PCOS (FSH may be normal or low-normal with high LH:FSH ratio)
- Kallmann syndrome (anosmia + hypogonadism)
Signs & Symptoms to Watch For
How to Prepare for This Test
In women, FSH should ideally be drawn on cycle day 2 or 3 (the early follicular phase) for ovarian reserve assessment. No fasting required.
Factors That Can Affect Results
- Cycle day in women (FSH varies dramatically throughout the menstrual cycle)
- Recent oral contraceptive use (suppresses FSH)
- Clomiphene citrate treatment (raises FSH)
- Biotin supplements (can interfere with immunoassays)
Related Topics
Frequently Asked Questions
What FSH level indicates menopause?
An FSH above 25 mIU/mL measured on cycle day 2–3 is suggestive of diminished ovarian reserve. An FSH above 40 mIU/mL on two occasions (12 weeks apart) in a woman with absent periods for 12+ months confirms menopause. In clinical practice, symptoms and menstrual history are usually sufficient to diagnose menopause without FSH testing in women over 45.
What is the difference between FSH and AMH for measuring ovarian reserve?
Both measure ovarian reserve but in different ways. FSH (measured on day 2–3) rises as follicle number decreases, so a high FSH indicates poor reserve. AMH is produced by antral follicles and falls as follicle count decreases, so a low AMH indicates poor reserve. AMH has advantages: it can be measured on any cycle day, has less cycle-to-cycle variability, and better predicts response to IVF stimulation. Both together give the most complete picture.