Early and premature
The NHS calls it early menopause when regular periods stop before 45, and premature menopause before 40. The medical term for the latter is premature ovarian insufficiency, or POI: the ovaries no longer work as usual for that age.
More common than thought
Based on new data, the 2024 international guideline (ESHRE, ASRM, IMS) estimates that about 3.5 percent of women are affected, more than previously assumed. Causes can include genetics, illness or treatments such as chemotherapy and radiotherapy. Often the cause remains unclear.
How you might notice it
Periods become irregular or stop, sometimes with hot flushes, sleep problems or vaginal dryness. According to the 2024 guideline, a single raised FSH level above 25 IU/L together with the cycle changes is enough for the diagnosis. If in doubt, it's measured again or anti-Müllerian hormone is tested.
Why hormones are replaced here
When hormones are missing this early, the risk of osteoporosis and cardiovascular disease rises. That's why the NHS advises replacing them, with hormone therapy or the combined pill. This is different from hormone therapy at 55: it replaces what the body would otherwise still be making at this age. For women who can't take hormones, such as after certain breast cancers, there are other options.
Having children and support
Getting pregnant is harder, but not always impossible. The NHS mentions IVF with your own frozen eggs or donor eggs as options. The diagnosis hits many women hard, so counselling and support groups are explicitly part of care.