What Is Perimenopause? What Actually Changes, and When

Maine has the oldest population of any state. The Census Bureau’s Vintage 2023 estimates put its median age at 44.8 years, with New Hampshire second at 43.4. That makes a question often treated as niche elsewhere close to a mainstream one here: what is perimenopause? Perimenopause is the transition leading up to menopause, when the ovaries release hormones erratically and menstrual cycles begin to change. It usually starts in a woman’s mid to late 40s and lasts about four years on average, though the range runs from two to eight years. It does not end at the last period. Perimenopause continues until 12 months after the final menstrual period, the point at which menopause is confirmed, and the average age of menopause in the United States is 52.

That definition is tidier than the experience. Most women do not get a clean announcement that the transition has started. They get a cycle that arrives nine days early, a summer of waking at 3 a.m., a stretch of months where everything feels normal again, and then another round. This guide covers the shape of the whole thing. What the staging system actually measures, what the hormones are doing, which changes tend to come first, and which ones are worth a phone call rather than a wait-and-see.

What Is Perimenopause, and When Does It Start?

Researchers use a staging system called STRAW+10, published in 2012 by an international workshop on reproductive aging. It puts boundaries on a transition that otherwise has none. Under STRAW+10, perimenopause begins at the early menopausal transition and ends 12 months after the final menstrual period. The early stage is defined by a persistent difference of seven days or more in the length of consecutive cycles. The late stage is marked by a gap of 60 days or longer without a period, and that late stage runs one to three years on average. Vasomotor symptoms, meaning hot flashes and night sweats, are likely to occur during it.

Ages are where the sources genuinely disagree, and it is worth naming that rather than papering over it. The Office on Women’s Health says perimenopause usually starts in a woman’s mid to late 40s. The National Institute on Aging says most women begin the transition between 45 and 55. ACOG notes that the amount of estrogen the ovaries produce begins to fluctuate as early as a woman’s 30s and 40s, and describes perimenopause as possibly running from 45 to 55. The Menopause Society gives the normal age range of menopause itself as 46 to 55, and says about 90 percent of women will have reached it by 55.

The headline number has the same problem. NIA and the Office on Women’s Health both put the average age of menopause in the United States at 52. ACOG puts the average age of the last menstrual period at 51. Both figures are current and both come from credible bodies. If you have seen different numbers in different places, that is why.

One point everybody agrees on. You only know menopause has happened in hindsight. NIA’s framing is that a woman knows she has reached it only after a full year with no period and no spotting. There is no test that calls it in advance.

A Quarter of Maine’s Women Are in the Age Band

National wellness coverage will not put a state number on this, so here is one. Maine’s Office of the State Economist counted 39,224 women aged 45 to 49 and 45,843 aged 50 to 54 living in Maine in 2022. That is 85,067 women in the 45 to 54 band alone. Widen it to ages 40 to 59 and the count is 178,217, out of a total female population of 704,759, or about 25.3 percent of all Maine women.

Two caveats matter. Those are age counts, not a count of women currently in the transition. No source publishes menopausal status by state, and plenty of women inside that band sit on one side of it or the other. The band is not a hard boundary in either direction either.

What the numbers do show is scale. Roughly one in four women in this state falls in the years where the question comes up, and Maine and New Hampshire sit first and second on the national age table, so the share here runs higher than it would in most places. Eighteen states had a median age over 40 in 2023. This is one of the two oldest.

The Hormone Part, Without the Oversimplification

The common version of this story is that estrogen starts dropping in your 40s and keeps dropping. The measured version is different, and the difference explains a lot about why perimenopause feels so inconsistent.

The Study of Women’s Health Across the Nation (SWAN) tracked hormones in a large multi-ethnic cohort across the transition. Follicle-stimulating hormone, or FSH, begins rising about 6.1 years before the final menstrual period. Estradiol, the main form of estrogen in the reproductive years, does something else entirely. Its mean concentration does not change until roughly 2 years before the final period. Then it starts decreasing, hits its steepest rate of change right at the final period, and stabilises about 2.2 years afterward.

So for most of perimenopause, estrogen is not on a slope. It is unstable. ACOG uses the word fluctuate. The Menopause Society describes it as erratic production. Some cycles run high, some run low, and the swings can be wider than anything a woman experienced in her 20s or 30s. The sustained decline is a late-transition event, not an early one.

That mechanism is why a good month does not mean the transition is over, and a rough month does not mean it is accelerating. It is also why symptoms and cycle length can move in ways that seem disconnected from each other.

What Changes First, and What Comes Later

Cycle changes usually lead. That is the STRAW+10 early marker for a reason. Consecutive cycles differing by a week or more is the earliest reliable signal. ACOG describes a normal cycle as typically 24 to 38 days, with a period generally lasting up to 8 days, which gives a reference point for noticing when your own pattern has moved. Periods can get closer together, further apart, heavier, lighter, or several of those in the same year. Our guide to what irregular periods look like in perimenopause works through the patterns in more detail.

Hot flashes and night sweats are the symptoms most people associate with this stage. The Menopause Society cites one large, diverse US study finding that up to 80 percent of women experience them at some point during the menopause transition, with each episode typically lasting between one and five minutes. What surprises people is the length of the whole run. In SWAN, the median total duration of frequent vasomotor symptoms was 7.4 years. Among the 881 women with an observable final menstrual period, the median persistence after that final period was 4.5 years. Women who were premenopausal or early perimenopausal when they first reported frequent symptoms had the longest run of all, a median of more than 11.8 years. For the physiology, we covered what actually causes a hot flash separately.

Sleep is often the change that gets somebody to finally make an appointment, partly because it compounds everything else. Night sweats fragment sleep directly, and broken sleep makes mood and concentration worse the next day. That is its own subject and we treated it as one in the guide to sleep disruption during menopause. In this part of the country a seasonal piece stacks on top. A New England winter with a 4:15 p.m. sunset does no favors to a sleep schedule that is already unsteady, and the groundwork in our piece on sleeping well through a Maine winter applies here too.

Mood deserves plainer treatment than it usually gets. An eight-year longitudinal study of women with no history of depression found that high depressive-symptom scores were more than four times as likely during the menopausal transition as when the same women were premenopausal (odds ratio 4.29, 95% CI 2.39 to 7.72). A diagnosed depressive disorder was 2.5 times as likely (odds ratio 2.50). The women served as their own comparison group, which is what makes the finding hard to wave off as life circumstances.

Cognitive symptoms are common and generally less alarming than they feel. The Menopause Society reports that 40 to 60 percent of midlife women describe forgetfulness during the transition, and states that changes in cognitive performance are typically mild and within the limits of normal. It also notes that dementia at midlife is very rare. Worth knowing if the phrase brain fog has started to worry you.

The Changes You Cannot Feel

Two of the most consequential shifts in this window produce no symptoms at all, which is exactly why they belong in a general guide.

The first is bone. SWAN found that bone mineral density loss began about one year before the final menstrual period and decelerated about two years after it. Over a 10-year window, cumulative loss at the lumbar spine came to 10.6 percent, and 7.38 percent of that was lost inside the narrow band around the final period. At the femoral neck the cumulative figure was 9.1 percent, with 5.8 percent during the same window. Most of a decade of loss is concentrated in a few years, and none of it is perceptible while it happens. That is part of why we wrote about vitamin D and bone health as we age.

The second is cardiovascular. The American Heart Association’s 2020 scientific statement describes the menopause transition as a time of accelerating cardiovascular disease risk, documenting adverse changes in body composition, in lipids and lipoproteins, and in measures of vascular health across the transition. The statement’s own framing is that midlife is a critical window for early prevention. That is strong language from a body that does not use it casually, and it argues for treating this stage as a checkpoint rather than something to simply get through.

Why a Blood Test Usually Doesn’t Settle It

A reasonable instinct is to ask for a hormone panel. The Office on Women’s Health is direct about why that is not usually recommended. For most women, hormone levels go up and down in an unpredictable way during the transition, so it is difficult to tell from a blood test whether a woman has gone through menopause or is getting close to it. Providers do not usually recommend the test unless there is a medical reason.

The STRAW+10 authors do note that FSH greater than 25 IU/L in a random blood draw is characteristic of being in the late transition. That describes a stage rather than diagnosing one, and it says little in the years before it. Given that FSH starts rising roughly six years out while estradiol stays flat for most of that stretch, a single draw can land almost anywhere.

There is a different reason a clinician may run labs, and it is a good one. Hypothyroidism produces symptoms that overlap with perimenopause, including fatigue and heavy or irregular menstrual periods. NIDDK reports that nearly 5 out of 100 Americans aged 12 and older have hypothyroidism, that women are much more likely than men to develop it, and that it is more common among people older than age 60. Ruling that in or out is a different exercise from trying to time the menopause transition, and it is worth doing.

What Warrants a Conversation With a Clinician

Irregular is expected. Some patterns are not, and ACOG names them specifically: bleeding or spotting between periods, bleeding or spotting after sex, periods that last more than a week, periods happening very close together, and any bleeding after menopause. ACOG also defines heavy bleeding as soaking through one or more tampons or pads every hour for several hours in a row, and notes that it can cause iron-deficiency anemia. None of that is cause for alarm on its own. All of it is a reason to book an appointment instead of waiting to see whether it settles.

Age matters too. The Menopause Society says about three in 100 women go through menopause before age 40, and advises that women under 40 who have missed three or more menstrual periods see a healthcare professional to check for primary ovarian insufficiency.

Contraception is the item most often missed. Pregnancy is still possible during perimenopause, and irregular cycles do not change that. NIA advises that a woman who does not want to get pregnant continue using birth control for at least a full 12 months after her last period. The Menopause Society gives the same advice, framed as using contraception until menopause is confirmed at one year after the final menstrual period.

A few things shift the timeline. NIA notes that smoking is associated with an earlier onset of menopause and more severe menopausal symptoms, and that symptom experience varies by race and ethnicity. Black women are more likely to have an early onset, to experience more symptoms, and to have symptoms for longer, while Asian women are less likely to have troubling symptoms.

As for what to do about any of it, that conversation belongs with a clinician who knows your history. ACOG and The Menopause Society both describe hormone and non-hormone categories of treatment for managing symptoms, and choosing between them turns on individual medical history in a way no article can decide for you. Over-the-counter products are a separate question, and we looked at what the evidence actually supports in our review of supplements marketed for perimenopause.

The useful thing to take from all of this is that the transition has a shape. A beginning you can identify by cycle length. A middle where hormones swing rather than fall. A late stage where the decline is real and the symptoms tend to peak. And an endpoint that is only visible a year after it happens. Knowing the shape does not make it shorter. It does make it easier to tell an ordinary chapter from a reason to pick up the phone.

Sources

• U.S. Census Bureau. Nation Continues to Age as It Becomes More Diverse (Vintage 2023 Population Estimates), press release CB24-TPS.34. https://www.census.gov/newsroom/press-releases/2024/population-estimates-characteristics.html
• Maine Office of the State Economist. Maine State and County Population Projections to 2042. https://www.maine.gov/dafs/economist/sites/maine.gov.dafs.economist/files/inline-files/MaineStateCountyPopulationProjections2042.xlsx
• National Institute on Aging. What Is Menopause? https://www.nia.nih.gov/health/menopause/what-menopause
• Office on Women’s Health, U.S. Department of Health and Human Services. Menopause basics. https://womenshealth.gov/menopause/menopause-basics
• Harlow SD, Gass M, Hall JE, et al. Executive summary of the Stages of Reproductive Aging Workshop + 10. Journal of Clinical Endocrinology and Metabolism. 2012;97(4):1159-68. https://pmc.ncbi.nlm.nih.gov/articles/PMC3319184/
• Randolph JF Jr, Zheng H, Sowers MR, et al. Change in follicle-stimulating hormone and estradiol across the menopausal transition. Journal of Clinical Endocrinology and Metabolism. 2011;96(3):746-54. https://pubmed.ncbi.nlm.nih.gov/21159842/
• Avis NE, Crawford SL, Greendale G, et al. Duration of menopausal vasomotor symptoms over the menopause transition. JAMA Internal Medicine. 2015;175(4):531-9. https://pubmed.ncbi.nlm.nih.gov/25686030/
• The Menopause Society. Menopause Symptoms. https://menopause.org/patient-education/menopause-topics/symptoms
• The Menopause Society. Perimenopause. https://menopause.org/patient-education/menopause-topics/perimenopause
• The Menopause Society. Premature Menopause. https://menopause.org/patient-education/menopause-topics/premature-menopause
• American College of Obstetricians and Gynecologists. Perimenopausal Bleeding and Bleeding After Menopause. https://www.acog.org/womens-health/faqs/perimenopausal-bleeding-and-bleeding-after-menopause
• American College of Obstetricians and Gynecologists. Heavy Menstrual Bleeding. https://www.acog.org/womens-health/faqs/heavy-menstrual-bleeding
• Greendale GA, Sowers M, Han W, et al. Bone mineral density loss in relation to the final menstrual period in a multiethnic cohort: results from the Study of Women’s Health Across the Nation (SWAN). Journal of Bone and Mineral Research. 2012;27(1):111-8. https://pubmed.ncbi.nlm.nih.gov/21976317/
• Freeman EW, Sammel MD, Lin H, Nelson DB. Associations of hormones and menopausal status with depressed mood in women with no history of depression. Archives of General Psychiatry. 2006;63(4):375-82. https://pubmed.ncbi.nlm.nih.gov/16585466/
• El Khoudary SR, Aggarwal B, Beckie TM, et al. Menopause Transition and Cardiovascular Disease Risk: Implications for Timing of Early Prevention. A Scientific Statement From the American Heart Association. Circulation. 2020;142(25):e506-e532. https://pubmed.ncbi.nlm.nih.gov/33251828/
• National Institute of Diabetes and Digestive and Kidney Diseases. Hypothyroidism (Underactive Thyroid). https://www.niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism

This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before making any health decisions.