Menopause
and Perimenopause

Menopause is a natural biological event that every woman experiences — the point at which the ovaries stop releasing eggs and oestrogen (the primary female sex hormone) production falls significantly. It is defined as twelve consecutive months without a menstrual period. What comes before that point is perimenopause (the transitional phase, often lasting several years), and what comes after is postmenopause (the rest of life beyond that point).

In the UK, the average age at which menopause occurs is 51, with most women reaching it between the ages of 45 and 55.^[1] But the transition typically begins earlier than that — perimenopause usually starts in the mid-to-late 40s, with hormone levels beginning to fluctuate unpredictably before periods stop altogether.^[1]

Perimenopause — the transition phase

Perimenopause (from the Greek peri, meaning "around") is the phase leading up to the final period. During this time, the ovaries begin producing less oestrogen and progesterone (the hormone that prepares the womb lining for pregnancy), but not consistently — levels fluctuate, sometimes quite dramatically, from month to month and even day to day. Periods may become irregular — shorter, longer, heavier, lighter, or more widely spaced. Menopause-associated symptoms often begin during this phase, sometimes before any change in periods is noticed at all.

Perimenopause can last anywhere from a few months to over a decade. There is no reliable way to predict its duration for any individual woman. It ends once twelve months have passed without a period, at which point menopause is confirmed retrospectively.

Postmenopause

Postmenopause refers to all the years that follow. Oestrogen levels stabilise at a lower level — not zero, but significantly reduced compared to reproductive years. For many women, the more acute vasomotor symptoms (hot flushes and night sweats — see Key Terms below) improve over time. But the lower oestrogen environment continues to have effects on bone density, cardiovascular risk, and genitourinary health (see Section 2).

Surgical and medically induced menopause

Menopause can also occur as a result of surgery (bilateral oophorectomy — surgical removal of both ovaries) or certain medical treatments, including chemotherapy and radiotherapy directed at the pelvic area. In these cases, menopause is immediate rather than gradual, and symptoms are often more abrupt and severe, because the hormone change happens suddenly rather than over several years.

Premature ovarian insufficiency and early menopause

Premature ovarian insufficiency (POI — reduced or absent ovarian function) affects around 1 in 100 women and occurs before age 40.^[2] Early menopause (between ages 40 and 44) affects between 3% and 8% of women.^[3] Both carry specific long-term health implications — particularly for cardiovascular health and bone density — because oestrogen deficiency occurs at a younger age than expected. NICE NG23 recommends that women with POI be offered HRT (hormone replacement therapy — see Key Terms below) and continued on it until at least the average age of natural menopause, unless there is a contraindication (a medical reason not to use it).

Vasomotor symptoms — hot flushes and night sweats

Hot flushes are the most recognised symptom of menopause — a sudden sensation of intense warmth, usually beginning in the chest and rising to the face and neck, often accompanied by reddening of the skin and followed by sweating and chills. Night sweats are the same phenomenon occurring during sleep, often waking women repeatedly and significantly disrupting sleep quality. Around 80% of women experience these symptoms to some degree.^[5] For many women, they are mild and manageable. For others, they are severe — frequent, disabling, and substantially affecting quality of life and the ability to work.

Sleep, mood, and cognition

Sleep disruption from night sweats is one of the most commonly reported impacts of perimenopause. Sustained poor sleep has downstream effects on mood, concentration, memory, and emotional resilience. Many women also report cognitive symptoms directly — commonly described as brain fog, difficulty finding words, and a sense that memory and mental sharpness have reduced. Low mood, anxiety, and irritability are also frequently reported, and appear to have both a hormonal basis (oestrogen has direct effects on mood-regulating neurotransmitters — chemical messengers in the brain) and a secondary basis through sleep deprivation and the cumulative impact of persistent symptoms.

Genitourinary syndrome of menopause (GSM)

Falling oestrogen levels affect the tissues of the vagina, vulva, and urinary tract — causing them to become thinner, drier, and more fragile. This can lead to vaginal dryness, itching, discomfort or pain during sexual intercourse, and urinary symptoms including urgency, frequency, and a greater tendency to urinary tract infections (UTIs — bladder infections). Unlike vasomotor symptoms, which often improve with time, GSM tends to persist and can worsen without treatment. It is substantially undertreated — many women are unaware that effective, safe local treatments exist, and many are reluctant to raise it.

Bone density

Oestrogen plays a critical role in maintaining bone density — the structural strength of bones. When oestrogen falls sharply at menopause, bone is lost at an accelerated rate. Research published in the New England Journal of Medicine found that mean annual bone mineral density loss in postmenopausal women was 1.9%.^[6] Over time, this loss accumulates into osteopenia (reduced bone density, see Key Terms) and osteoporosis (low bone mass — bone mineral density T-score of −2.5 or below — increasing the risk of fragility fractures — fractures caused by forces that would not break a healthy bone). One in three women aged 50 and over will experience a fragility fracture during their remaining lifetime.^[6]

Cardiovascular health

Oestrogen has a protective effect on the cardiovascular system — it supports healthy blood vessel function and influences cholesterol profiles. After menopause, this protection diminishes, and cardiovascular risk rises. Women's risk of heart disease increases significantly in postmenopause, and by older age, women's cardiovascular disease rates converge with — and in some conditions exceed — those of men. The timing of any hormonal intervention matters here, which is discussed in Section 3.

Work and quality of life

Menopause is now recognised as a significant occupational health issue. Women aged 45–55 represent the fastest-growing group in the UK workforce. Severe symptoms affect the ability to concentrate, maintain performance, manage work relationships, and in some cases lead women to reduce hours, turn down promotion, or leave employment altogether. The combined impact of vasomotor symptoms, poor sleep, cognitive symptoms, and mood change can be substantial — and for many women, deeply isolating, partly because the connection between what they are experiencing and menopause goes unrecognised for years.

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