Am I in Perimenopause? The Signs to Look For in Your Late 30s and Early 40s

Most women expect perimenopause in their early fifties. But for a significant proportion, the first signs arrive in their late 30s or early 40s — and they look nothing like hot flushes. Here is what to look for and what to do when you notice it.

The timing mismatch between when perimenopause actually starts and when most women expect it to start is one of the most significant contributors to the years of unrecognised, undiagnosed, and untreated perimenopause that so many women experience. The cultural image of menopause — a woman in her early fifties having hot flushes — has become the template against which women measure their own experiences. And when their experiences do not fit that template, they look for other explanations.

Nearly half of women globally are unaware of perimenopause before they begin experiencing it. This is not ignorance or inattention — it is the predictable consequence of a cultural and medical education that has consistently misdated and mischaracterised the transition. For women in their late 30s or early 40s who are experiencing significant symptoms, the possibility that perimenopause is the cause frequently does not occur to them — because they have been told, implicitly or explicitly, that perimenopause is something that happens to older women.

It is not.

When Perimenopause Actually Starts

The research on perimenopause onset is more complex than the cultural narrative suggests. The average age at which perimenopause symptoms begin is approximately 47 — but the range is wide, and many women begin experiencing symptoms considerably earlier.

The SWAN study, one of the largest and most comprehensive longitudinal studies of women across the menopause transition, found that the menopausal transition — the period of hormonal change that precedes the final period — can begin as early as the late 30s in some women. Studies consistently show that between 5% and 10% of women reach menopause before age 45, and the perimenopause transition that precedes it typically begins several years before the final period.

For women under 40 who experience symptoms consistent with perimenopause, the clinical term is premature ovarian insufficiency (POI), which is a distinct condition warranting specific investigation and management. But for women in their late 30s and early 40s, the onset of perimenopause is within the normal range — not early, not unusual, but entirely consistent with what the research shows about the actual (as opposed to culturally assumed) timing of the transition.

The Early Signs That Are Almost Never Mentioned

The early signs of perimenopause in women in their late 30s and early 40s are rarely hot flushes. They are typically psychological and cognitive — changes that are easy to attribute to stress, overwork, relationship difficulties, or simply the accumulation of adult responsibilities.

Increased anxiety that feels qualitatively different from previous anxiety is one of the most consistent early signs. Women describe it as more physical, more sudden, less connected to circumstances, and arriving at unusual times — particularly between 2am and 4am. This is the anxiolytic effect of progesterone declining before oestrogen has dropped enough to produce obvious vasomotor symptoms. The anxiety arrives first because progesterone's calming effect diminishes first.

Unexplained low mood or a sense of flatness — not full depression, but a reduction in the experience of pleasure and motivation that is difficult to attribute to specific circumstances — is another early sign. The relationship between oestrogen and dopamine means that as oestrogen begins to fluctuate, the reward and pleasure pathways of the brain are affected. Activities that previously felt satisfying or enjoyable may begin to feel effortful or neutral. This is frequently and incorrectly attributed to burnout, relationship dissatisfaction, or early-onset depression.

Brain fog — the specific cognitive slowing, word-finding difficulty, and memory unreliability described in detail in our brain fog article — often appears before significant vasomotor symptoms. Because the women experiencing it are in their late 30s or early 40s, it tends to be dismissed or attributed to overwork, stress, or insufficient sleep. All of which may also be present — but the hormonal contribution to cognitive change is real and specific, and it typically precedes the more obviously hormonal symptoms.

Changes to the menstrual cycle — which can begin years before the cycle becomes visibly irregular — include changes to cycle length (either shorter or longer than previous), changes to flow (heavier, lighter, or more erratic), more pronounced pre-menstrual symptoms than previously, and spotting at unusual points in the cycle. Many women dismiss these changes as insignificant or attribute them to stress. They are worth noting.

Reduced libido, changes to genital sensation or lubrication, and the beginning of the genitourinary changes associated with declining oestrogen can all appear in the early perimenopause years. These changes are often attributed to relationship factors or attributed to getting older — neither of which is incorrect as a contributing factor, but neither of which identifies the hormonal driver.

Joint pain and stiffness — particularly in the hands and wrists — is one of the less-known early perimenopause symptoms. Oestrogen has anti-inflammatory effects in joint tissue, and its decline during perimenopause can produce joint discomfort that is easily attributed to overuse or early arthritis. It often improves significantly with HRT.

The 52 Symptoms You Are Probably Not Looking For

Beyond the better-known symptoms, perimenopause has 52 documented symptoms spanning every body system. Many of these are almost never discussed in mainstream conversations about the transition, and women experiencing them have no way of connecting them to perimenopause because the connection is never communicated.

Electric shock sensations — a brief, sharp electrical feeling typically experienced in the head, neck, or extremities — are experienced by a significant proportion of perimenopausal women and are almost universally alarming when they occur without explanation. They are entirely harmless and directly related to oestrogen's effects on neurological function, but they are rarely included in the perimenopause symptom lists that women encounter.

Formication — the sensation of insects crawling under or on the skin — is another symptom that causes significant distress when it is not understood. It is caused by oestrogen's role in skin nerve sensitivity and is a recognised perimenopause symptom. Itchy ears, tinnitus, gum changes, and changes to taste and smell are similarly documented but rarely communicated.

Heart palpitations — an awareness of the heartbeat as irregular, racing, or skipping — are caused by oestrogen's effect on the autonomic nervous system, which regulates heart rate. They are almost always benign in the context of perimenopause but should always be assessed clinically to rule out cardiac causes. They are consistently frightening in the moment and frequently lead women to A&E convinced they are experiencing a cardiac event.

The Blood Test Problem

The most common barrier women in their late 30s and early 40s encounter when presenting to their GP with perimenopause symptoms is the reliance on blood tests to confirm or exclude the diagnosis. The conversation frequently goes: "Your FSH is normal, so you can't be in perimenopause."

This is incorrect, and it misapplies clinical guidance. FSH (follicle-stimulating hormone) and oestradiol levels fluctuate dramatically during perimenopause — which is, by definition, a period of hormonal fluctuation rather than stable decline. A blood test taken on one day may appear entirely normal even in a woman with significant perimenopause symptoms. The same woman's blood test taken two weeks later might show very different results. A single normal blood test does not exclude perimenopause.

The NICE 2024 guideline is explicit that perimenopause should be diagnosed on the basis of symptoms and history for women over 45, and that blood tests are not required. For women under 45, blood testing can be more informative — particularly for ruling in or out premature ovarian insufficiency — but a normal blood test in this age group still does not definitively exclude perimenopause.

What to Do When You Suspect Perimenopause

The most useful immediate action is systematic symptom tracking. A comprehensive 52-symptom checklist — covering all documented perimenopause symptoms across every category — gives you a complete picture of what you are experiencing and makes the connections that individual symptoms, assessed in isolation, may not suggest.

A symptom timeline, looking back over when things started to change, helps establish the duration and progression of your symptoms. When did the anxiety start? When did sleep begin to deteriorate? When did the brain fog arrive? This retrospective picture is often more revealing than women expect — they frequently discover that what they thought were isolated, recent changes have actually been building for several years.

Tracking your cycle and the symptoms that cluster around different phases can reveal the hormonal structure of your symptom experience. The pre-menstrual amplification pattern — symptoms significantly worse in the week before the period — is one of the clearest early indicators of perimenopause and is diagnostically useful for the clinical conversation.