What happens to your hormones in perimenopause

In perimenopause, the ovaries do not simply switch off. As the supply of follicles dwindles, the signals between the brain and the ovaries become erratic: FSH climbs, estrogen swings between high and low, and progesterone drops in the cycles where no egg is released. Average estrogen does not fall much until the last two years before your final period, which is why symptoms can begin while blood tests still look normal.

The chain reaction

The changes follow a sequence that starts inside the ovary. A 2007 review of the Melbourne Women’s Midlife Health Project, one of the long-running studies that measured hormones repeatedly through the transition, describes it this way:

1. Follicles decline. The number of ovarian follicles falls with age. This is the root cause of everything that follows.
2. AMH and inhibin B fall. Both are made by follicles. Anti-Mullerian hormone (AMH) tracks the size of the remaining pool, and inhibin B normally helps restrain FSH.
3. FSH rises. With less inhibin B, the pituitary releases more follicle-stimulating hormone. The higher FSH appears to help keep estradiol up until late in reproductive life.
4. The system becomes unstable. The review calls the transition “a time of marked hormonal instability,” and that instability, more than any steady decline, shapes the experience of perimenopause.

Hormone changes over time

The clearest timeline comes from SWAN, which measured FSH and estradiol every year in 1,215 women until their final menstrual period.

Hormone	About 6 years before the final period	2 to 6 years before	Final 2 years	After the final period
FSH	Begins to rise	Rising gradually	Rises fastest	Stabilizes at a high level about 2 years after
Estradiol (average)	Unchanged	Unchanged, with surges and dips in individual cycles	Falls, fastest at the final period	Low; stabilizes about 2 years after
Progesterone	Normal in ovulatory cycles	Lower as cycles without ovulation become more common	Low in most cycles	Minimal, since ovulation has stopped
AMH and inhibin B	Declining	Declining	Very low	Undetectable

Two details from SWAN stand out. The overall pattern was the same regardless of the age at which women reached their final period, their race or ethnicity, or whether they smoked. And obesity blunted the FSH rise and delayed its start to about 5.5 years before the final period, one reason a single FSH value is hard to interpret.

Estrogen: a rollercoaster, not a slide

The common shorthand is that estrogen falls in perimenopause. On average, it does not, at least not until late. In SWAN, mean estradiol did not change until about 2 years before the final period, then fell, reaching its fastest rate of decline at the final period.

Averages hide the swings. Researchers who took blood three times a week from 77 women found that in 11 of 29 ovulatory cycles during the transition (37%), estradiol rose a second time in the second half of the cycle and peaked around the next period. They called this a luteal out-of-phase event. These cycles had lower progesterone and were linked to unusually short cycles, under 21 days, or long ones, over 40 days. The researchers concluded that many of the marked increases in estradiol and much of the cycle irregularity in the transition may come from these events, apparently triggered by prolonged high FSH.

In plain terms, high FSH can recruit a new follicle too early, producing an extra burst of estrogen on top of an existing cycle. Periods of relatively high estrogen alternate with stretches of low estrogen, sometimes within weeks.

Progesterone: the quieter change

Progesterone is made mainly after ovulation, by the structure left behind when an egg is released. When a cycle has no ovulation, there is little progesterone.

A study of 108 women who collected daily urine samples over five years tracked this directly. Cycles without ovulation became steadily more common across perimenopause, and more than 60% of cycles in late perimenopause were anovulatory. FSH and LH were higher and estrogen metabolites lower in those cycles. Total progesterone output fell in late perimenopause, and even in cycles with ovulation, peak progesterone declined steadily across the transition.

Bleeding often changes along with these hormone shifts, sometimes becoming heavier or longer. See heavy bleeding and clots for when bleeding needs attention.

FSH: the brain pushes harder

FSH is the brain’s signal to the ovary to grow a follicle. As the ovary responds less readily, FSH rises. In SWAN, the FSH rise began about 6 years before the final period and accelerated about 2 years before it. Because FSH responds to what the ovary is doing that month, its level can look menopausal one month and normal the next. Our guide to why hormone tests are often normal explains what this means for testing.

Testosterone: a slower, separate story

Testosterone does not follow the perimenopause pattern. In a community study of 1,423 women aged 18 to 75, total and free testosterone, DHEA sulfate and androstenedione all declined steeply with age, with the biggest drops in the earlier decades of adult life. Among women aged 45 to 54, menopausal status had no independent effect on androgen levels. The ovary continues to produce testosterone after menopause, and women whose ovaries were surgically removed had lower levels. If low desire is your concern, see testosterone and libido.

After the final period

The instability settles. The Melbourne review describes postmenopause as a state of markedly raised FSH and low estradiol, with inhibin B and AMH undetectable. In SWAN, both FSH and estradiol reached stable levels about 2 years after the final period.

What this means for you

• Symptoms can start before estrogen falls. Night sweats, sleep disruption, mood change and heavier periods can all appear while average estrogen is still in the normal range, driven by swings and lower progesterone.
• Staging uses your cycle, not your blood. The STRAW+10 system defines the stages of the transition by bleeding patterns and is meant to apply regardless of age, ethnicity, body size or lifestyle. See what perimenopause is for the stages.
• Treatment does not have to wait. Because symptoms reflect fluctuation, options that smooth hormone levels or treat specific symptoms can be used during perimenopause. A clinician can review them with you; search for an ob-gyn near you, or start with the symptom check.