FSH (follicle-stimulating hormone): what it is, what it tells you and when it’s tested

FSH is a hormone made by the pituitary, a small gland at the base of the brain. In women it makes follicles grow in the ovaries; in men it helps produce sperm. When the ovaries respond less, as they do towards menopause, the pituitary makes more of it and FSH rises.

When it’s tested

Doctors order it when periods become irregular or stop, when a pregnancy is slow to come, or when they suspect an early menopause. In men, usually for fertility problems or low testosterone.

If you still have periods, it is usually done between day two and day four of the cycle, together with oestradiol. Over 45, it is usually not needed to tell whether you are in perimenopause or menopause: your symptoms and your periods are enough.

It is not a test for people who feel well, which is why Rosa does not test it. Instead it looks at what often changes in the menopause years: ferritin and haemoglobin if your periods are heavy, TSH and LDL cholesterol.

What it tells you, and what it does not

A high FSH says your ovaries respond less and your pituitary is pushing harder to make them work. Towards menopause this is normal.

It does not say when your last period will be. In perimenopause FSH goes up and down from month to month: a high value can be normal again the next month, and a normal value does not rule out that the transition has started.

Nor does it say whether you can get pregnant. Age matters more.

That is why it is read together with other tests:

Normal FSH levels

There is no single normal value. In women FSH changes with the phase of the cycle and with age, and every lab prints its own intervals, usually split by phase: follicular, ovulatory, luteal and postmenopausal.

That is why the day of the test matters. Read your value against the interval for the right phase, on your own report.

Towards menopause FSH rises and swings. An FSH above 25 mIU/mL, with periods skipped for more than two months, is typical of the late part of the transition. After menopause it stays high.

In men the values are steadier. There too, the interval on your report is what counts.

If your FSH is high or low

High FSH before 40

If you are under 40 and your periods become rare or stop, your doctor may think of premature ovarian insufficiency, a menopause that comes early. International guidelines consider it with irregular or absent periods and an FSH above 25 mIU/mL.

It is not rare: it affects a few women in a hundred. It is worth finding early, because years with little oestrogen weigh on bones and heart, and hormone treatment helps.

If there is doubt, your doctor repeats the test or adds anti-Müllerian hormone.

What can skew the result

A few things change FSH without saying much about your ovaries. It helps to know them before your blood test.

When to worry

Talk to your doctor or gynaecologist if:

Frequently asked questions

Does a high FSH mean I am in menopause? Not necessarily. In perimenopause FSH goes up and down. Menopause is confirmed after a year without periods. Over 45 a doctor usually recognises it from your symptoms, without tests.

On which day of the cycle is FSH tested? If you have periods, usually between day two and day four, counting the day your period starts as day one. If you have no periods, on any day.

What are FSH levels after menopause? After menopause FSH is high, usually above 25 mIU/mL. Your report prints its lab’s postmenopausal interval.

Can you get pregnant with a high FSH? Yes, it can happen. In a study of women aged 30 to 44 with no known fertility problems, those with an FSH above 10 got pregnant naturally as often as the others. Age matters more. If you are trying for a pregnancy, talk to your gynaecologist.

What is the difference between FSH and LH? They come from the same gland and work as a pair. FSH makes follicles grow, LH triggers ovulation. Towards menopause both rise, FSH more.

Does Rosa test FSH? No. Rosa measures ferritin, haemoglobin, TSH and LDL cholesterol, which are useful to follow in the menopause years. If your doctor wants FSH, they order it separately.

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