There is no single test
People often expect a blood test to settle the question. In practice, the hormone that would be measured, follicle-stimulating hormone, swings so much from day to day during the transition that a single reading is unreliable, which is why testing it is not recommended for women aged 45 and over with typical symptoms (NICE guideline NG23, 2024). Perimenopause is recognised clinically, from the story your body is telling, not from a number.
What to actually look for
The two things that matter most are a change in your menstrual cycle and the arrival of new symptoms that fit. Periods becoming shorter, longer, heavier, lighter, or less predictable is often the first sign. Alongside that, women commonly notice some mix of hot flushes, night sweats, broken sleep, low mood or irritability, brain fog, joint aches, and changes in libido (Journal of Clinical Endocrinology & Metabolism, 2021).
For many women the very first clue is not a hot flush at all, but a run of poor sleep or a dip in concentration turning up around the same time as their cycle starting to shift.
The stage you are in is read from both of these together. Your cycle pattern leads, but the symptoms you have, how many and how intense they are, add to the picture. Hot flushes and night sweats, for example, tend to be most frequent and strongest in late perimenopause and the first year or two after your periods stop, so a heavier symptom load often points to a later stage (Journal of Clinical Endocrinology & Metabolism, 2021).
| Stage | What your cycle does | Symptoms often seen | Typical timing |
|---|---|---|---|
| Late reproductive years | Cycles still fairly regular, perhaps slightly shorter | Few or none | Early to mid 40s |
| Early perimenopause | Cycle length varies by seven days or more between cycles | First hot flushes, lighter sleep and mood shifts, often mild | Mid to late 40s |
| Late perimenopause | Periods skip, with gaps of sixty days or more | Hot flushes and night sweats usually most frequent and strongest | The one to three years before your last period |
| Postmenopause | Twelve months with no period at all | Many symptoms ease, though some can linger | From around 51 on average |
Doctors map these with a system called STRAW, reading your cycle pattern first and the number and severity of your symptoms alongside it. For women over 45, this is usually enough, and a blood test is not normally needed.
The age question
Age changes the approach. From 45 onward, symptoms and cycle changes are usually enough to recognise perimenopause without tests. Between 40 and 45, a doctor may consider blood tests in some circumstances. Under 40, symptoms that suggest menopause need proper assessment rather than being assumed, as they warrant a different pathway (NICE guideline NG23, 2024).
When to talk to a doctor
See your doctor if symptoms start before 45, if periods become very heavy or close together, if there is bleeding between periods or after sex, or if symptoms are affecting your daily life and you want to discuss options. A diagnosis is not the only reason to go, support is. anna does not diagnose, and this article is not medical advice.
