Menopause is a single day: twelve months after your final period, identified in retrospect. Perimenopause is everything leading up to it, and it can run for four to ten years. Most of what women describe as menopause symptoms happen during perimenopause, while periods are still occurring.
Oestrogen does not simply decline
The common mental model — a gentle downward slope — is wrong, and the mismatch explains a great deal of confusion. During perimenopause the ovaries respond erratically to increasingly loud pituitary signals. Oestradiol swings, and some of those swings go higher than anything in a normal cycle before crashing.
That volatility is why symptoms fluctuate week to week, why a woman can feel entirely normal for a month and then not, and why a blood test taken on a good day can look unremarkable.
The symptoms beyond hot flushes
Vasomotor symptoms — hot flushes and night sweats — are the recognised signature. They are not the most common complaint, and they are frequently not the most disruptive.
- Sleep disruption, especially waking at 3–4am, often without a night sweat to explain it
- Anxiety, low mood, irritability and a sense of reduced resilience
- Brain fog — word-finding difficulty and short-term memory lapses that can be genuinely frightening
- Joint aches, often mistaken for early arthritis
- Cycle changes — shorter, longer, heavier, lighter, skipped
- Vaginal dryness and urinary symptoms, which unlike the others do not improve without treatment
- Palpitations, migraines, tinnitus, dry eyes, itchy skin
The psychological symptoms are frequently the first to appear, and frequently misattributed. Women in their early forties presenting with new anxiety and poor sleep are often treated for anxiety without the timing being considered.
How it is actually diagnosed
| Your age | How NICE says to diagnose |
|---|---|
| Over 45 | On symptoms and cycle changes alone. No blood test needed. |
| 40–45 | On symptoms, with FSH as supporting evidence if the picture is unclear. |
| Under 40 | FSH on two occasions, four to six weeks apart. Premature ovarian insufficiency needs proper investigation and treatment. |
So what is testing for?
Not for confirming perimenopause. For excluding the conditions that look exactly like it — and this is genuinely valuable, because they are common and treatable.
- Thyroid disease — fatigue, low mood, brain fog, temperature intolerance, cycle changes. Considerably more common in women.
- Iron deficiency — heavy perimenopausal bleeding is a frequent and under-recognised cause. Produces fatigue, breathlessness and poor concentration.
- Raised prolactin — a treatable cause of irregular or absent periods.
- Low vitamin D — contributes to fatigue and low mood, and matters for bone health as oestrogen falls.
Sources
NICE NG23: Menopause — diagnosis and management
Diagnosis on symptoms alone in women over 45; guidance against routine FSH testing; POI investigation under 40.
British Menopause Society tools for clinicians
Symptom range, perimenopausal hormone variability and differential diagnosis.
