Summary
Follicle-Stimulating Hormone (FSH) is released by the pituitary gland to stimulate egg development in women and sperm production in men. In women, FSH is a key marker of ovarian reserve and menopausal status — it rises sharply as the ovaries fail. In men, elevated FSH indicates impaired sperm production. FSH is interpreted alongside LH and the sex hormones it regulates.
In women, FSH stimulates the growth of ovarian follicles each cycle. As ovarian reserve declines with age, the ovaries respond less readily, so the pituitary secretes more FSH to compensate. A raised early-cycle (day 2–5) FSH therefore signals diminished ovarian reserve, and persistently high FSH supports a diagnosis of menopause.
In men, FSH acts on the Sertoli cells of the testes to support sperm production. High FSH with low sperm count indicates primary testicular failure; low FSH suggests a pituitary or hypothalamic problem.
FSH is interpreted together with LH and the relevant sex hormones (oestradiol in women, testosterone in men) to localise the problem to the gonads (primary) or the pituitary/hypothalamus (secondary).
What It Is
FSH is a glycoprotein gonadotropin secreted by the anterior pituitary gonadotroph cells under the pulsatile control of hypothalamic gonadotropin-releasing hormone (GnRH). It shares a common alpha subunit with LH, TSH, and hCG, with a distinct beta subunit conferring specificity.
In women, FSH drives granulosa cell proliferation and follicular maturation, and stimulates aromatase to produce oestradiol. In men, FSH acts on Sertoli cells to support spermatogenesis and inhibin B production. Inhibin and sex steroids provide negative feedback on FSH secretion.
Reference ranges (women): follicular phase 3.5–12.5 IU/L; mid-cycle peak 4.7–21.5 IU/L; postmenopausal 25.8–134.8 IU/L. Men: 1.5–12.4 IU/L. An early follicular FSH > 10–12 IU/L suggests reduced ovarian reserve.
Functions
Follicle and egg development
FSH stimulates ovarian follicles to grow and mature each cycle, driving egg development and oestradiol production.
Sperm production
In men, FSH supports the Sertoli cells of the testes to maintain healthy sperm production.
Ovarian reserve marker
Rising early-cycle FSH reflects declining ovarian reserve — a key marker in fertility assessment.
Menopause indicator
Persistently high FSH supports a diagnosis of menopause as ovarian function ceases.
Reference Ranges
FSH — Follicle-Stimulating Hormone
Measured in IU/L| Status | Range (IU/L) | What it means |
|---|---|---|
| Low | < 3.5 | Low FSH — suggests pituitary/hypothalamic suppression (secondary hypogonadism). |
| Normal (follicular) | 3.5–12.5 | Normal early-cycle range in women; normal range in men. |
| Reduced reserve | 12.5–25 | Elevated early-cycle FSH — suggests diminished ovarian reserve. |
| Menopausal | > 25 | High FSH — consistent with menopause or primary gonadal failure. |
Female ranges depend on cycle phase and menopausal status. Measure on day 2–5 with oestradiol for ovarian reserve. Persistently high FSH supports menopause. Interpret with LH and sex hormones.
Symptoms of Imbalance
FSH abnormalities reflect the state of the ovaries or testes and the pituitary; symptoms relate to the underlying reproductive disturbance.
- Absent or irregular periods (women)
- Low libido
- Infertility
- Reduced testicular size (men)
- Symptoms of pituitary dysfunction
- Fatigue
- Hot flushes and menopausal symptoms (women)
- Irregular or absent periods
- Infertility
- Reduced sperm count (men)
- Symptoms of ovarian insufficiency
Causes of Imbalance
- Hypothalamic dysfunction (stress, low body weight, excessive exercise)
- Pituitary disease or tumour
- Hyperprolactinaemia
- Kallmann syndrome (congenital GnRH deficiency)
- Anabolic steroid use (suppresses gonadotropins)
- Menopause and perimenopause
- Premature ovarian insufficiency
- Primary testicular failure (men)
- Turner syndrome
- Klinefelter syndrome (men)
- Chemotherapy or radiotherapy-induced gonadal damage
FAQs
In women, a raised early-cycle (day 2–5) FSH suggests the ovaries are becoming less responsive — a sign of diminished ovarian reserve. The pituitary produces more FSH to try to stimulate the ovaries. This can make conception more difficult and is an important factor in fertility planning. AMH is often measured alongside FSH as a more stable indicator of egg supply.
A persistently high FSH, together with low oestradiol and 12 months without periods, supports a diagnosis of menopause. However, during perimenopause FSH fluctuates considerably from cycle to cycle, so a single result can be misleading. In women over 45, menopause is usually diagnosed on symptoms alone, with blood tests reserved for younger or uncertain cases.
FSH and LH are both pituitary gonadotropins, and their pattern localises the problem. If both are high, the issue lies in the ovaries or testes (primary gonadal failure). If both are low, the issue lies in the pituitary or hypothalamus (secondary hypogonadism). Measuring them together, with the relevant sex hormone, gives a clear picture of where the disturbance originates.
In men, FSH supports sperm production. A high FSH with a low sperm count indicates that the testes are failing to respond properly — primary testicular failure, which can result from genetic conditions (such as Klinefelter syndrome), previous infection, injury, or cancer treatment. A low FSH instead points to a pituitary or hypothalamic cause.
References
- Practice Committee of the American Society for Reproductive Medicine. Testing and interpreting measures of ovarian reserve. Fertil Steril. 2020;114(6):1151–1157. View source
- Burger HG. Diagnostic role of FSH measurements during the menopausal transition. Climacteric. 2007;10(Suppl 2):27–32. View source
- Jungwirth A, et al. European Association of Urology guidelines on male infertility. Eur Urol. 2012;62(2):324–332. View source