A hormone produced by the pituitary gland that stimulates ovarian follicles to develop. Levels rise as ovarian function declines, which is why it is measured in menopause assessment, though a single reading cannot confirm or exclude perimenopause.
What FSH does
FSH is released by the pituitary gland in the brain and signals the ovaries to develop follicles, each containing an egg. The developing follicles produce estrogen.
Estrogen feeds back to the pituitary and suppresses further FSH release. This feedback loop keeps the system balanced during the reproductive years.
As the supply of follicles depletes, the ovaries respond less, estrogen production falls, and the feedback signal weakens. The pituitary responds by releasing more FSH. This is why FSH rises as menopause approaches.
Why a single reading is unreliable in perimenopause
During perimenopause the ovaries respond inconsistently. A cycle in which a follicle develops normally produces enough estrogen to suppress FSH; the next cycle may not.
As a result FSH can measure high one week and within the normal range the next, in the same person. A raised reading does not confirm perimenopause, and a normal reading does not exclude it.
Home menopause test kits measure FSH, usually in urine, and carry the same limitation regardless of how the result is presented.
When measuring FSH is useful
- Under the age of forty-five, and particularly under forty, where menopause is not assumed and requires evaluation. Persistently raised FSH alongside stopped periods supports a diagnosis of early menopause or primary ovarian insufficiency.
- Where the usual bleeding pattern is unavailable, such as after hysterectomy with the ovaries retained.
- Where the clinical picture is atypical and other explanations need ruling in or out.
- In women over forty-five with typical symptoms, FSH testing is not usually required, because the diagnosis rests on history and the twelve-month rule.
How results are interpreted
There is no single threshold that confirms menopause in someone still having periods. Interpretation depends on age, symptoms, cycle history and whether the result is repeated.
Where testing is indicated, a raised result is usually repeated after an interval rather than acted on alone.
Hormonal contraception suppresses FSH, so results taken during use are not interpretable in the usual way.
Related measurements
- Luteinizing hormone (LH) is released by the same gland and also rises in menopause, though it adds little beyond FSH in this context.
- Estradiol is the main form of estrogen measured in blood. It falls as menopause approaches but fluctuates in the same way as FSH.
- Anti-Mullerian hormone (AMH) reflects remaining ovarian reserve and is used in fertility assessment. It is not a test for perimenopause and does not predict when symptoms will begin.
When to seek medical advice
- Periods stopping or becoming very irregular before the age of forty-five, which warrants evaluation rather than a home test
- A raised FSH result acted on without repeat testing or clinical assessment
- Symptoms that are severe or atypical, which warrant assessment regardless of any hormone result
Common misconceptions
| Misconception | Truth |
|---|---|
| A high FSH confirms menopause. | In someone still having periods it does not. Levels fluctuate during perimenopause, and a raised reading can be followed by a normal one. |
| A normal FSH means nothing is happening. | It does not exclude perimenopause. Symptoms are the more reliable guide in women over forty-five. |
| Home FSH kits give a definitive answer. | They measure the same fluctuating hormone as a blood test, so a result in either direction does not settle the question. |
Frequently asked questions
Follicle-stimulating hormone, released by the pituitary gland to stimulate ovarian follicles to develop. Levels rise as ovarian function declines, which is why it is measured in menopause assessment.
There is no single threshold that confirms menopause in someone still having periods, because levels fluctuate. Interpretation depends on age, symptoms, cycle history and repeat testing.
Developing follicles produce estrogen, which normally suppresses FSH release. As follicles deplete, estrogen falls, the suppressing signal weakens, and the pituitary releases more FSH.
They measure FSH reliably enough, but FSH itself fluctuates during perimenopause. A single reading in either direction does not confirm or exclude the transition.
Under forty-five, and particularly under forty, where menopause requires evaluation. Also where the bleeding pattern is unavailable, such as after hysterectomy with ovaries retained, or where the picture is atypical.
Usually not. In women over forty-five with typical symptoms, diagnosis rests on history and the twelve-month rule rather than on testing.
Yes. Hormonal contraception suppresses FSH, so results taken during use cannot be interpreted in the usual way.
FSH rises as ovarian function declines and is used in menopause assessment. AMH reflects remaining ovarian reserve and is used in fertility assessment; it does not predict symptom onset.
Routine repeat hormone testing is not usually helpful. Treatment decisions in menopause are generally guided by symptoms rather than by target numbers.
Estradiol, the main form of estrogen in blood, and sometimes luteinizing hormone. Thyroid function and a full blood count are frequently more useful, since both overlap with menopause symptoms.
