Follicle-stimulating hormone

What it is

Follicle-stimulating hormone (FSH) is a glycoprotein hormone produced by the anterior pituitary gland that governs reproductive development and function in both sexes, with a normal adult female range of roughly 3.5–12.5 mIU/mL in the follicular phase and values above 25 mIU/mL on two separate tests used clinically to confirm menopause. Also called follitropin, FSH belongs to the gonadotropin family alongside luteinizing hormone (LH), thyroid-stimulating hormone (TSH), and human chorionic gonadotropin (hCG) — all of which share an identical alpha subunit while differing in their beta subunit. In Canada, FSH is measured through standard serum panels available at LifeLabs and Dynacare, and the test is covered under provincial health insurance when ordered for medically indicated reasons such as infertility workup, menopause assessment, or delayed puberty.

FSH levels begin rising approximately six years before the final menstrual period, making the hormone one of the earliest measurable signals of the menopausal transition. A single elevated reading is rarely sufficient for diagnosis; clinicians typically confirm menopause with two FSH values above 25–30 mIU/mL drawn at least four to six weeks apart, alongside clinical history.

Population	Typical FSH range
Adult male	1.5–12.4 mIU/mL
Female, follicular phase (days 1–10)	3.5–12.5 mIU/mL
Female, mid-cycle surge	4.7–21.5 mIU/mL
Female, luteal phase	1.7–7.7 mIU/mL
Postmenopausal female	25.8–134.8 mIU/mL
Prepubertal child (either sex)	0–4.0 mIU/mL

Ranges vary by laboratory and assay; always interpret results against the reference interval on your specific lab report.

Causes and mechanism

The hypothalamus releases gonadotropin-releasing hormone (GnRH) in pulses into the hypophyseal portal circulation. Low-frequency GnRH pulses preferentially stimulate FSH secretion from gonadotropic cells in the anterior pituitary; high-frequency pulses shift output toward LH. This pulse-frequency tuning is why continuous GnRH agonists — such as leuprolide, used in Canada for endometriosis and prostate cancer — paradoxically suppress FSH and LH after an initial flare.

In women, rising estrogen from developing follicles suppresses FSH through negative feedback, while the protein inhibin B (secreted by granulosa cells) provides an additional brake. As ovarian reserve declines with age, inhibin B and estrogen fall, removing that brake and allowing FSH to climb. In men, Sertoli cells in the testes secrete inhibin B in response to FSH, completing an analogous negative-feedback loop.

Abnormally high FSH can reflect primary gonadal failure (the gonads are not responding), while abnormally low FSH points toward a hypothalamic or pituitary problem — a distinction that guides the entire diagnostic workup.

Symptoms and diagnosis

FSH itself does not produce symptoms directly; it is the hormonal consequences of FSH dysregulation that patients notice. Elevated FSH in women is associated with irregular or absent periods, hot flashes, night sweats, vaginal dryness, and reduced fertility. In men, high FSH alongside low testosterone may present as fatigue, reduced libido, or infertility. Low FSH in either sex can cause amenorrhea, delayed puberty, or hypogonadotropic hypogonadism.

The FSH blood test requires a simple venous draw. For women of reproductive age, clinicians typically request the sample on cycle day 2 or 3 to capture the follicular-phase baseline. No fasting is required. In Canada, the test is often ordered alongside LH, estradiol, and anti-Müllerian hormone (AMH) when assessing ovarian reserve or fertility.

A day-3 FSH above 10 mIU/mL is generally considered borderline for ovarian reserve; values above 15–20 mIU/mL are associated with poor response to ovarian stimulation in assisted reproduction. These thresholds are used by Canadian fertility clinics but are not universally standardized across all provincial guidelines.

Treatment options

FSH itself is not treated — the underlying condition driving the abnormal level is. That said, FSH-based medications are central to several therapies:

• Ovarian stimulation for IVF: Recombinant FSH products (follitropin alfa, follitropin beta) and urinary-derived gonadotropins are injected to stimulate multiple follicle development. These are available in Canada by prescription and are partially covered under some provincial fertility programs (Ontario's OHIP+ IVF program, for example, covers one funded cycle for eligible patients).
• Hypogonadotropic hypogonadism: When low FSH is the problem, exogenous gonadotropin therapy can restore fertility in both men and women.
• Menopausal hormone therapy (MHT): Estrogen-based MHT suppresses elevated FSH as a secondary effect, though FSH normalization is not the primary treatment goal. The Society of Obstetricians and Gynaecologists of Canada (SOGC) supports MHT for symptomatic menopause in appropriate candidates.
• GnRH agonists/antagonists: Used to deliberately suppress FSH in conditions like endometriosis, uterine fibroids, and hormone-sensitive cancers.

When to see a clinician in Canada

Request an FSH test through your family physician or nurse practitioner if you are experiencing irregular periods, signs of early menopause before age 45, difficulty conceiving after 12 months of unprotected sex (or 6 months if over 35), or signs of delayed puberty in a child. Referral to a reproductive endocrinologist or gynecologist is appropriate when FSH results are outside the expected range and fertility or hormonal management is being considered.

For Canadians without a family physician, virtual care platforms — including Maple, Felix, Cleo, and others — can order initial hormone panels and provide referrals. Wait times for reproductive endocrinology vary by province; in some regions, patients wait 6–18 months for a specialist appointment, making early GP-ordered testing valuable.

Limitations and open questions

Research is still emerging on FSH's role beyond reproduction. Recent studies suggest that elevated FSH in the menopausal transition may directly contribute to central adiposity, bone loss, and possibly cognitive changes — independent of estrogen decline — but these findings are preliminary and have not yet changed clinical guidelines. Health Canada has not issued specific guidance on FSH as a standalone cardiovascular or metabolic risk marker.

The optimal FSH threshold for diagnosing diminished ovarian reserve remains debated; different fertility clinics use cutoffs ranging from 10 to 20 mIU/mL, and AMH is increasingly preferred as a more stable marker because it does not fluctuate across the menstrual cycle the way FSH does. Additionally, FSH assays are not fully standardized across Canadian laboratories, meaning a result from one lab may not be directly comparable to a result from another — always interpret values against the reference range provided by the specific laboratory that processed the sample.