Premature menopause: age cut-off and raised FSH
Premature menopause, also called premature ovarian insufficiency, is the loss of normal function of the ovaries (which release an egg each month and make oestrogen) before the age of 40.
Remember
Under the age of 40, the diagnosis rests on compatible symptoms (such as hot flushes) plus follicle-stimulating hormone (FSH, which drives egg development in the ovary) being raised on two separate samples taken at least 4 weeks apart, with thyroid function and prolactin (a pituitary hormone that can stop periods when it is high) measured to exclude other causes.
The cut-off for premature menopause is the age of 40 years. Menopause between 40 and 45 years is usually called early menopause, and natural menopause arrives at an average age of 51, confirmed once 12 months have passed without a period. In premature menopause, ovarian activity can be intermittent (on and off), and the loss of function is not always permanent.
When the ovaries fail, oestrogen falls. The pituitary gland (the gland at the base of the brain) then loses negative feedback, the braking effect that oestrogen normally has on it, and releases more follicle-stimulating hormone (FSH), which stimulates the follicles (the egg-containing structures in the ovary). A raised FSH therefore points to ovarian failure.
Compatible symptoms, such as hot flushes and absent or infrequent periods, are read alongside blood tests. FSH varies from one sample to the next, so a single raised result may be a passing change. In a woman under 40, two samples taken at least 4 weeks apart must both be raised to support the diagnosis.
Thyroid function and prolactin (a pituitary hormone that can stop periods when it is high) are measured as well. Abnormalities in either can temporarily disrupt ovarian function, so these tests are used to exclude other causes. In ovarian failure FSH is high, not low.
Getting this right matters, since years without oestrogen can lead to more severe osteoporosis and atherosclerosis (thinning of the bones and hardening of the arteries).
Key facts
- Premature
- Ovarian function is lost before the age of 40 years.
- Early
- Menopause between 40 and 45 years is usually called early menopause.
- Natural menopause
- It averages age 51 and is confirmed after 12 months without a period.
- Diagnostic pattern
- In a woman under 40 with compatible symptoms, FSH must be raised on both of two samples taken at least 4 weeks apart.
- Single result
- FSH varies, so one raised result may be a passing change.
- Other tests
- Thyroid function and prolactin are checked to exclude other causes that can temporarily disrupt ovarian function.
- FSH direction
- High FSH suggests the ovaries have failed, whereas low FSH suggests a problem in the hypothalamus or pituitary gland (the brain centres that drive the ovaries).
Exam traps
- A single raised FSH result does not support premature menopause on its own, because FSH varies and one raised value may be a passing change. A second sample taken at least 4 weeks later also needs to be raised.
- Abnormal thyroid function tests do not show that the ovaries have failed, because thyroid disease is a different and potentially treatable cause of disturbed periods. Thyroid function is checked to exclude other causes, not to confirm premature menopause.
- Loss of ovarian function between 40 and 45 years is usually called early menopause, not premature menopause, because the cut-off for premature menopause is before 40.
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