Follicle Stimulating Hormone (FSH) Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Follicle Stimulating Hormone?

Follicle stimulating hormone (FSH) is a gonadotropin produced by the anterior pituitary gland in the brain. In women, FSH stimulates the growth and maturation of ovarian follicles during the menstrual cycle, playing a central role in ovulation and fertility. In men, FSH supports spermatogenesis by acting on Sertoli cells in the testes.

FSH levels are regulated by a feedback loop involving the hypothalamus, pituitary gland, and gonads (the HPG axis). When oestrogen or testosterone levels are low, the pituitary increases FSH secretion to stimulate the gonads. Conversely, adequate sex hormone levels suppress FSH through negative feedback.

In women, FSH levels fluctuate throughout the menstrual cycle: low in the luteal phase, rising in the early follicular phase to recruit follicles, peaking at mid-cycle alongside LH to trigger ovulation. After menopause, FSH rises significantly (often above 30 IU/L) because the ovaries no longer produce enough oestrogen to suppress it.

Why Is FSH Tested?

• Fertility assessment — FSH on day 2–5 of the menstrual cycle indicates ovarian reserve
• Menopause confirmation — elevated FSH (>30 IU/L on two occasions) confirms menopause
• Irregular periods investigation — FSH helps distinguish between hypothalamic, pituitary, and ovarian causes
• Male infertility — high FSH in men suggests primary testicular failure
• Delayed or precocious puberty — FSH helps evaluate pubertal development
• PCOS evaluation — FSH is typically normal or low in PCOS, with an elevated LH:FSH ratio

Normal Ranges

In women, FSH should ideally be tested on day 2–5 of the menstrual cycle for fertility assessment. Timing is critical for accurate interpretation.

What Do High FSH Levels Mean?

• Menopause or perimenopause — the most common cause of elevated FSH in women over 40
• Premature ovarian insufficiency — loss of ovarian function before age 40
• Diminished ovarian reserve — FSH above 10 IU/L on day 3 suggests reduced egg quantity
• Primary testicular failure — in men, damage from chemotherapy, radiation, or Klinefelter syndrome
• Turner syndrome — chromosomal condition (45,X) causing ovarian dysgenesis
• Ovarian surgery or chemotherapy — damage to ovarian tissue raises FSH

What Do Low FSH Levels Mean?

• Hypothalamic amenorrhoea — stress, extreme weight loss, or excessive exercise suppresses GnRH, reducing FSH
• Pituitary disorders — tumours, surgery, or Sheehan syndrome impair FSH secretion
• PCOS — FSH is often at the lower end of normal relative to LH
• Hyperprolactinaemia — elevated prolactin suppresses GnRH and FSH
• Anabolic steroid use — exogenous androgens suppress the HPG axis
• Pregnancy — FSH is naturally suppressed during pregnancy

How to Improve Your FSH Levels

• Address hypothalamic causes — if FSH is low due to stress or under-eating, restoring adequate nutrition and reducing exercise intensity can restore normal cycling
• Maintain healthy body weight — both underweight and obesity disrupt the HPG axis
• Manage stress — chronic stress elevates cortisol, which suppresses GnRH and FSH
• Discuss fertility treatments — if FSH is high and ovarian reserve is low, IVF with FSH injections may be discussed
• Supplement wisely — vitamin D, DHEA, and CoQ10 are being studied for ovarian reserve support
• Avoid endocrine disruptors — BPA, phthalates, and pesticides may interfere with reproductive hormones

When Should You Get Tested?

• You are trying to conceive and want to assess ovarian reserve
• You have irregular or absent periods
• You are experiencing menopausal symptoms (hot flushes, night sweats)
• Men with low sperm count or infertility
• As part of a comprehensive hormone assessment

Which Lola Health Tests Include FSH?

FSH is included in our Hormone 7 panel alongside LH, oestradiol, progesterone, testosterone, SHBG, and prolactin. Available as an add-on with any Lola Health blood test.