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In perimenopause, estrogen swings before it falls, progesterone drops as ovulation slows and FSH rises. Learn what each hormone does and how it causes symptoms.
During perimenopause, the ovaries respond less consistently to signals from the brain. Follicle-stimulating hormone (FSH) rises. Estrogen swings, sometimes higher than usual, before it declines. Ovulation becomes less frequent, so progesterone falls in many cycles. These fluctuations, more than a steady drop, explain why perimenopause symptoms can be so unpredictable.
| Hormone | What it does | What happens in perimenopause |
|---|---|---|
| Estradiol (the main estrogen) | Builds the womb lining; supports bones, blood vessels, skin, vaginal tissue, brain and temperature control | Swings widely, sometimes higher than usual, before declining in late perimenopause |
| Progesterone | Prepares and stabilizes the womb lining after ovulation; has calming effects on the brain | Falls in cycles where ovulation does not happen |
| Follicle-stimulating hormone (FSH) | Signals from the brain that stimulate follicles to grow | Rises as the ovaries respond less, but varies considerably |
| Luteinizing hormone (LH) | Triggers ovulation | Rises later; the ovulation surge becomes less reliable |
| Inhibin B | Made by growing follicles; normally keeps FSH in check | Falls early, which allows FSH to rise |
| Anti-Müllerian hormone (AMH) | Reflects the number of remaining follicles | Falls steadily and becomes undetectable around menopause |
| Testosterone | Contributes to sex drive, energy and muscle | Declines gradually with age from your 20s onward, rather than dropping sharply at menopause |
Estrogen is spelled "oestrogen" in the UK.
The number of follicles in the ovaries falls throughout life. By the 40s, fewer follicles are growing each month, so they make less inhibin B. With less inhibin B holding it back, FSH starts to rise.
At this stage, the higher FSH works as compensation. Research from the Melbourne Women’s Midlife Health Project suggests the rise in FSH helps keep estradiol at near-normal levels until late in reproductive life. Periods may still look regular.
As follicle numbers fall further, the system becomes less stable:
This is the stage when cycles begin to vary by a week or more. See early signs of perimenopause.
Ovulation becomes much less common. One long-term study found that the share of cycles with ovulation fell from about 60% to under 10% over the six years before the final period. In the final year, 60% to 70% of cycles either do not involve ovulation or have an unusually long first half.
Gaps between periods lengthen to 60 days or more, and estrogen begins a more sustained decline. See how long perimenopause lasts for the full timeline. Research tracking women over time found that AMH and inhibin B fall to undetectable levels about five years before the final period, while FSH roughly doubles.
Estrogen continues to fall and may not reach its lowest point until one to two years after the final period. FSH is then consistently high, while inhibin B and AMH are undetectable.
Not everyone goes through the gradual changes described above:
If you have had any of these treatments, ask your care team what hormone changes to expect and what support is available.
Because perimenopause is defined by fluctuation, a blood test shows only one moment. You could have a normal FSH one week and a high one the next, or an estrogen level that is higher than usual even though you have symptoms.
This is why the UK’s National Institute for Health and Care Excellence (NICE) advises against using hormone tests to identify perimenopause in people aged 45 or over who have typical symptoms. A normal result does not rule perimenopause out, and a single high result does not confirm it. See perimenopause tests.
You may see perimenopause described as a "hormone imbalance" that can be fixed with specific supplements, diets or detailed hormone panels. A few points are worth knowing:
If a product promises to "balance your hormones," ask what evidence supports it and whether it has been tested in people in perimenopause.
The right choice depends on your symptoms, health history and preferences. For an overview, see our perimenopause guide.
Both. Estrogen often swings higher and lower than usual during perimenopause, before falling more steadily in late perimenopause and after the final period.
Lower progesterone is expected in perimenopause because ovulation happens less often. It isn’t used to diagnose perimenopause, because levels depend on where you are in your cycle and whether you ovulated that month.
Testosterone declines gradually with age, mostly before menopause, rather than falling sharply at menopause. Surgical removal of the ovaries is an exception, as it causes a more sudden drop.
No. Hormone levels vary too much during the transition to predict how long it will last or when your final period will be.
Editorial status: evidence-based educational article; not individually medically reviewed. Last evidence check: September 10, 2026.
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