Perimenopause: What Is Actually Happening

Most women in perimenopause are not low on estradiol. They are swinging on it, and short on the hormone that used to hold it steady. Here is the mechanism, what it does to her, and what to ask for.

A patient came to me this week. She is 45. She asked her doctor to check her hormones and was told, "No, you're 45. You're not in perimenopause."

Another asked her OB-GYN about her libido, which had gone. She was told there was nothing to be done about that, and that she could try watching some porn.

What they say to me is quieter than either of those. "I just don't feel like myself." "I just feel off."

They are right, and there is a measurable reason.

One note on words, because it changes what a study is reporting. Estrogen on its own usually means conjugated equine estrogen, made from horse urine. Estradiol means the bioidentical molecule a woman's own body makes, 17-beta estradiol. Older papers use estrogens as a catch-all, a third meaning again.

The governor comes off

Her ovary runs with a speed governor on it, a hormone called inhibin. Its job is to hold down FSH, the signal from the brain that drives the ovary. In her forties the inhibin falls first.

Take the governor off and the signal climbs. The ovary gets driven harder than it ever has been, and estradiol does not fall. It spikes.

This was measured in exactly the woman who gets turned away. Ten women aged 40 to 45, all still cycling regularly and still ovulating, were compared against women in their twenties. Their inhibin B was lower, their FSH was higher, and their early-cycle estradiol was higher, not lower.

At scale it looks the same. SWAN followed 3,302 women for more than twenty years and found that for nearly half of them estradiol climbs in the years before the final period, and only then falls steeply.

What does collapse is ovulation. No ovulation means no corpus luteum, and the corpus luteum is the only thing that makes real progesterone. So she is high and unsteady on estradiol with nothing left to hold it down.

That is the whole picture. She is not running out of estradiol. She is running out of progesterone.

The fog is real, and somebody measured it

The brain fog is not a figure of speech and not her imagination. Researchers scanned 54 women aged 40 to 65 with a tracer that binds the estrogen receptor itself, so the scan counts the receptors sitting there waiting.

Receptor density went up through the transition, not down. The receptors are there. What arrives erratically is the hormone. And the women with the highest receptor density had the worst memory scores and the worst symptoms.

Her brain is not broken. It is understaffed.

"There are no labs for that"

There is no single blood test that says perimenopause. A Melbourne study that tracked women through the whole transition concluded there is no single reliable hormonal marker of menopausal status for an individual woman.

That is not an argument for testing nothing. It is an argument against reading one number and sending her home. The field's own staging system does what I do: it stages her on cycle history first and treats a hormone level as supporting evidence.

So I take the history seriously, I look at a panel rather than a single value, and I repeat it. One snapshot is not a diagnosis. Estradiol drawn on a random day in a cycling woman tells you almost nothing, because the number depends entirely on the day you drew it.

And the diagnosis that matters is clinical. The lab tells me when she has finished the transition. It does not tell me whether she is suffering.

What I actually give her

Progesterone, first, and continuously. Two hundred milligrams of oral micronized progesterone at bedtime is my baseline, and I go up by symptoms. It is the hormone that actually left. It is cheap, it has been available for decades, and it is the one she is least likely to be offered.

I never cycle it. Progesterone ten or twelve days a month leaves eighteen days with nothing opposing her own estradiol, and the fall at the end of each course is its own event. The trial that settled this gave estradiol and progesterone together every single day for a year. Among 1,255 women who had an evaluable biopsy at twelve months, no endometrial hyperplasia was found. The reviewers called it the first rigorous trial to demonstrate that continuous progesterone protects the lining. An international expert panel had already put the continuous oral starting dose at 200 mg a day.

Those women were postmenopausal, taking one milligram of prescribed estradiol. My patient is making her own, persistently, in surges, with nothing opposing it. She has more unopposed estradiol than they did and she gets more progesterone than the trial used.

Thyroid and testosterone get looked at. Perimenopause and low thyroid share almost the whole symptom list, so I check free T3 and treat by symptoms rather than TSH alone. Testosterone gets the same dose she would get after menopause. There is no reduction for perimenopause, whatever she is told elsewhere.

And not estradiol. Not yet.

Women arrive on estradiol all the time, prescribed for real symptoms, bloated, tender, bleeding and short-tempered. She is already high, so adding more treats the wrong end of the problem. Take it away, put her on a real dose of progesterone, and the symptoms usually go with it.

There is a second reason. In an anovulatory year her lining is under estradiol with no progesterone to finish the job, and it builds quietly. Nothing announces that.

What to ask for

If you are told you are too young, or that there are no labs, ask for four things. Ask for your cycle history to be taken seriously, including cycles that still arrive on time. Ask for more than one set of labs. Ask for micronized progesterone by name, because it is bioidentical progesterone and not the same thing as a progestin. And ask if they are going to treat your symptoms or your lab values.

You are not asking for anything exotic. You are asking for the hormone you stopped making.

What it means

The transition is not a bad week. Hot flashes alone run a median of about seven and a half years, and for women whose symptoms start early they run past eleven. Nobody should spend a decade being told she is fine.

She is not crazy, she is not too young, and she is not low on estradiol. She is short on progesterone, and that has an answer.

The whole argument:

⚠️ Educational content, not individual medical advice, diagnosis or a treatment recommendation. Nothing here tells any woman what to take, and nobody should start, stop or change a prescription because of an article. Your own labs and history belong in a one on one.

🩺 DNP led telehealth hormone optimization. Book a consultation and find everything: withinyou.health/links

Sources

Archer DF, et al. A combined, bioidentical, oral, 17beta-estradiol and progesterone capsule for the treatment of moderate to severe vasomotor symptoms due to menopause. Expert Rev Clin Pharmacol. 2019;12(8):739-751. (Review of the REPLENISH trial.)

Avis NE, et al. Duration of menopausal vasomotor symptoms over the menopause transition. JAMA Intern Med. 2015;175(4):531-539.

Burger HG, et al. Prospectively measured levels of serum FSH, estradiol, and the dimeric inhibins during the menopausal transition in a population-based cohort of women. J Clin Endocrinol Metab. 1999;84:4025-4030.

El Khoudary SR, et al. The menopause transition and women's health at midlife: a progress report from the Study of Women's Health Across the Nation (SWAN). Menopause. 2019;26(10):1213-1227.

Harlow SD, et al. Executive summary of the Stages of Reproductive Aging Workshop +10: addressing the unfinished agenda of staging reproductive aging. Menopause. 2012;19(4):387-395.

Klein NA, et al. Decreased inhibin B secretion is associated with the monotropic FSH rise in older, ovulatory women. J Clin Endocrinol Metab. 1996;81(7):2742-2745.

Lobo RA, et al. A 17beta-estradiol-progesterone oral capsule for vasomotor symptoms in postmenopausal women: a randomized controlled trial. Obstet Gynecol. 2018;132(1):161-170. (REPLENISH. Postmenopausal women, 1 mg estradiol, manufacturer sponsored, 12 months.)

Mosconi L, et al. In vivo brain estrogen receptor density by neuroendocrine aging and relationships with cognition and symptomatology. Sci Rep. 2024;14:12680.

Stute P, et al. The impact of micronized progesterone on the endometrium: a systematic review. Climacteric. 2016;19(4):316-328.