During menopause, your ovaries run out of functional follicles, and the hormones they once produced drop sharply. But estrogen doesn’t simply fall off a cliff one day. The process unfolds over several years, with different hormones changing at different times, some dropping, some rising, and some fluctuating unpredictably. Understanding this sequence helps explain why menopause symptoms can start years before your final period and linger well after it.
The Ovaries Slowly Run Out of Follicles
At birth, your ovaries contain roughly 500,000 to 1,000,000 primordial follicles. These are tiny sacs that each hold an immature egg. Throughout your reproductive life, follicles are steadily used up or reabsorbed, and this degeneration actually accelerates as you age. By the time you reach menopause, the ovaries are virtually depleted. This follicle loss is the central event driving every other hormonal change.
The earliest measurable sign of declining follicle reserves isn’t a drop in estrogen. It’s a drop in two lesser-known hormones: inhibin B and anti-Müllerian hormone. Both are produced by the follicles themselves, and their decline signals that the pool is shrinking. This can begin years before your periods change noticeably.
Estrogen: A Bumpy Decline, Not a Straight Line
Most people assume estrogen simply decreases during perimenopause. The reality is more chaotic. In the early stages of the menopausal transition, estrogen levels are often preserved or even elevated. This happens because your brain, sensing fewer responsive follicles, ramps up its signals to the ovaries, sometimes pushing estrogen production higher than normal in an attempt to force ovulation.
As the transition continues, estrogen swings become wider and more erratic. You might have a cycle with very high estrogen followed by one where levels crash. These wild fluctuations, more than the eventual decline itself, drive many of the symptoms women experience in their 40s. By the postmenopausal period, once your final period is at least 12 months behind you, estrogen drops to very low levels and stays there.
Progesterone Drops Earlier Than You Might Expect
Progesterone is only produced in meaningful amounts after ovulation. As the menopausal transition progresses, cycles without ovulation become increasingly common, which means progesterone production falls even while estrogen may still be relatively normal. Research tracking women across the transition found that the probability of cycles without ovulation increases steadily through perimenopause, and even in cycles where ovulation does occur, peak progesterone output declines starting in the early transition, well before the final period.
When ovulation does happen during late perimenopause, it tends to occur much later in the cycle. One study found the average ovulation day shifted to cycle day 27 in late perimenopause, compared to the typical day 14 in younger women. This means the window of progesterone production shrinks even in ovulatory cycles. By postmenopause, with no ovulation occurring at all, progesterone drops to negligible levels.
This early loss of progesterone relative to estrogen creates a temporary imbalance. Estrogen without the counterbalancing effect of progesterone can lead to heavier periods, breast tenderness, and mood changes, symptoms many women notice in their early to mid-40s before they suspect menopause is approaching.
FSH and LH Surge in Response
Your brain and ovaries communicate through a feedback loop. The pituitary gland at the base of your brain releases follicle-stimulating hormone (FSH) and luteinizing hormone (LH) to tell the ovaries to produce estrogen and progesterone. When those ovarian hormones are circulating at healthy levels, they signal back to the pituitary to ease off. This is called negative feedback.
As ovarian follicles disappear and estrogen and inhibin B production drops, that “ease off” signal weakens. The pituitary responds by producing more and more FSH and LH, essentially shouting louder at ovaries that can no longer respond. FSH rises first and is the more dramatic increase. A single FSH reading above 30 IU/L is consistent with perimenopause or menopause, though levels can fluctuate widely during the transition, so a normal reading doesn’t rule it out.
Interestingly, after the initial postmenopausal spike, both FSH and LH gradually decline with age. This suggests that aging itself affects the brain’s hormone-producing signals, independent of what’s happening in the ovaries.
What Happens to Testosterone
Testosterone in women comes from two sources: the ovaries and the adrenal glands. Unlike estrogen, testosterone doesn’t plummet at menopause. During the transition, testosterone and a related hormone called androstenedione rise modestly, roughly two to threefold, partly because elevated LH stimulates both the ovaries and the adrenal glands.
Research suggests that the adrenal glands actually develop new receptors for LH during midlife, allowing them to pick up some of the hormonal slack as the ovaries wind down. After menopause, the adrenal glands become the primary source of the sex steroids your body still produces. The relative balance between these remaining hormones, which vary from woman to woman, likely influences individual differences in symptoms, body composition, and long-term health risks.
How These Shifts Cause Symptoms
Hot Flashes and Night Sweats
Your brain has a thermostat that keeps your body temperature within a narrow comfort zone, called the thermoneutral zone. Normally, small fluctuations in core temperature don’t trigger a sweating or shivering response. Estrogen withdrawal, combined with rising levels of a brain chemical called norepinephrine, dramatically narrows this zone. A temperature increase as small as a fraction of a degree can then trigger a full heat-dissipation response: blood vessels dilate, sweat pours out, and you feel an intense wave of internal heat. This is a hot flash. At night, the same mechanism causes drenching sweats that disrupt sleep.
Sleep Disruption
Progesterone has a natural sedating effect. It works through a breakdown product called allopregnanolone, which activates the same brain receptors targeted by many sleep and anti-anxiety medications. As progesterone declines, this calming influence weakens. The loss of progesterone’s effect on these receptors also helps explain why some postmenopausal women develop sleep-disordered breathing. Layer in night sweats, and it’s easy to see why sleep quality takes a significant hit.
Mood Changes
The erratic hormonal swings of perimenopause, not just low estrogen but the unpredictable cycling between high and low, affect brain chemistry in ways that increase vulnerability to anxiety and depression. Data from menopausal women also show that markers of insulin resistance correlate with both depression and sleep disturbances, suggesting that metabolic changes compound the mood effects of shifting hormones.
Bone Loss
Estrogen acts as a brake on the cells that break down bone. When estrogen drops, bone breakdown accelerates while bone building can’t keep pace. The result is a loss of 1 to 5% of bone mass per year during the first five to seven years after menopause. This is the window of most rapid bone loss and the reason osteoporosis risk rises sharply in postmenopausal women.
Metabolic Shifts
Cortisol levels tend to be higher in late menopause, and insulin resistance increases. Estrogen normally helps your cells respond efficiently to insulin. Without it, blood sugar regulation becomes less effective, and fat storage shifts toward the abdomen. These metabolic changes, combined with rising cortisol, contribute to the weight gain and body composition changes many women notice even when their diet and activity level haven’t changed.
When It Happens Early
The average age of menopause is 51, but the same process can occur prematurely. Loss of ovarian function before age 40 is called premature ovarian insufficiency, and it affects about 1 in 100 women. The diagnostic criteria include irregular or absent periods for at least four months along with an FSH level above 25 IU/L, confirmed with a repeat test four to six weeks later. Loss of ovarian function between ages 40 and 44 is classified as early menopause. In both cases, the hormonal changes are identical to typical menopause, just happening sooner, which means a longer lifetime of low estrogen and the health consequences that come with it.