Hormone Journal

Follicle-stimulating hormone

Also known as: FSH

Medically reviewed by Hormone Journal Editorial Team · Last reviewed 2026-05-17

Follicle-stimulating hormone (FSH) is a pituitary hormone that drives egg follicle growth in women and sperm production in men.

What it is

Follicle-stimulating hormone (FSH) is a pituitary hormone that drives egg follicle growth in women and sperm production in men. It is a glycoprotein — a protein with sugar chains attached — made of two subunits: an alpha subunit shared with luteinizing hormone (LH), thyroid-stimulating hormone (TSH), and human chorionic gonadotropin (hCG), and a beta subunit unique to FSH. The pituitary gland releases FSH into the bloodstream, where it travels to the ovaries or testes to carry out its effects.

Causes and mechanism

The hypothalamus (a region at the base of the brain) releases gonadotropin-releasing hormone (GnRH) in pulses into a small blood vessel network called the hypophyseal portal circulation. Those pulses reach the anterior pituitary, which then secretes FSH and LH. Pulse frequency matters: slow GnRH pulses favor FSH release, while fast pulses favor LH release.

FSH levels are kept in check by negative feedback:

  • In women: rising estrogen from growing follicles signals the pituitary to reduce FSH output.
  • In men: Sertoli cells inside the testes release inhibin B in response to FSH, which then feeds back to suppress further FSH secretion.

When the gonads produce less estrogen or inhibin B — as happens at menopause or with testicular dysfunction — FSH rises because that feedback brake is removed.

Symptoms and diagnosis

Abnormal FSH levels rarely cause symptoms on their own; instead, they signal an underlying condition. A clinician orders an FSH blood test to investigate:

  • Irregular or absent periods, infertility, or signs of early menopause in women
  • Low sperm count or undescended/underdeveloped testes in men
  • Early or delayed puberty in children

Reference ranges (serum, mIU/mL):

GroupApproximate normal range
Adult men1.5 – 12.4
Women, follicular phase3.5 – 12.5
Women, mid-cycle peak4.7 – 21.5
Women, postmenopause25.8 – 134.8

A day-3 FSH level above roughly 10 mIU/mL is commonly used as a marker of diminished ovarian reserve, though it is interpreted alongside anti-Müllerian hormone (AMH) and antral follicle count for a fuller picture. A persistently elevated FSH (above ~25–30 mIU/mL) on two tests at least 4–6 weeks apart, combined with absent periods for 12 months, supports a diagnosis of menopause.

Treatment options

FSH itself is not treated in isolation — the underlying condition guides management:

  • Infertility / ovulation induction: Injectable FSH preparations (e.g., follitropin alfa or beta) stimulate follicle development for intrauterine insemination or in vitro fertilization (IVF).
  • Hypogonadotropic hypogonadism (low FSH due to pituitary or hypothalamic failure): GnRH pulsatile therapy or combined FSH/LH injections can restore fertility in both sexes.
  • Menopause-related symptoms: Menopausal hormone therapy (MHT) addresses estrogen deficiency; it does not directly target FSH, but FSH falls as estrogen levels rise.
  • GnRH agonists (e.g., leuprolide): Continuous use paradoxically suppresses FSH and LH, used in endometriosis, uterine fibroids, and prostate cancer.

Emerging research suggests FSH may directly influence bone density and body composition during menopause transition, but clinical applications of FSH-blocking strategies remain investigational as of 2025.

When to see a clinician

Seek evaluation if you have: periods that stop for more than 3 months before age 45, difficulty conceiving after 12 months of unprotected sex (or 6 months if over 35), signs of puberty before age 8 in girls or age 9 in boys, or puberty that has not started by age 13 in girls or 14 in boys. A single FSH value is rarely diagnostic alone — timing in the menstrual cycle and concurrent hormone levels (LH, estradiol, AMH) are needed for accurate interpretation.

FAQs

What does a high FSH level mean?

A high FSH level usually means the pituitary is working harder than normal because the ovaries or testes are not responding adequately — a pattern called primary hypogonadism. In women, an FSH consistently above about 25–30 mIU/mL alongside absent periods suggests menopause or premature ovarian insufficiency (POI). In men, a level above 12.4 mIU/mL can indicate impaired sperm production or testicular failure. The result must always be interpreted with symptoms and other hormone levels.

What does a low FSH level mean?

Low FSH points to a problem in the hypothalamus or pituitary rather than the gonads — called secondary or hypogonadotropic hypogonadism. Causes include extreme weight loss, excessive exercise, pituitary tumors, or use of anabolic steroids. In adults, FSH below about 1.5 mIU/mL is considered low. Treatment targets the root cause; pulsatile GnRH or gonadotropin injections can restore fertility in many cases.

What is the difference between FSH and LH?

Both FSH and LH are gonadotropins released by the pituitary, but they have distinct roles. FSH mainly stimulates follicle growth in women and Sertoli cell function (supporting sperm maturation) in men. LH triggers ovulation and stimulates estrogen and testosterone production. Clinicians often order both together: a high FSH with a high LH-to-FSH ratio (above about 2:1) can suggest polycystic ovary syndrome (PCOS), while both being low points to a pituitary or hypothalamic problem.

Can FSH levels predict fertility or menopause timing?

FSH is one of several markers used to estimate ovarian reserve — the quantity and quality of remaining eggs. A day-3 FSH above roughly 10 mIU/mL suggests diminished reserve, but it has limited ability to predict the exact timing of menopause. Anti-Müllerian hormone (AMH) is now considered a more stable marker because it does not fluctuate as much across the menstrual cycle. No single test reliably predicts natural menopause onset to within less than a few years.

Is FSH testing covered by insurance?

In the United States, FSH blood tests are typically covered by insurance when ordered for a medically recognized indication such as infertility evaluation, irregular periods, suspected menopause, or delayed puberty — usually with a copay or after meeting a deductible. Coverage for FSH testing as part of routine wellness or direct-to-consumer panels varies widely by plan. The test itself generally costs $30–$100 without insurance depending on the laboratory. Always confirm coverage with your insurer before testing.

Sources

All glossary termsUpdated 2026-05-17