The receptionist rings at twenty to five on a Thursday and reads the result off a screen. Everything came back normal. Nothing to worry about.

You are forty-three. You have not slept past four in the morning since February. Your cycle ran to twenty-four days last month and thirty-six the month before. You put the phone down and you feel, on top of everything else, slightly foolish.

Here is what nobody said on that call. The test cannot answer the question you asked it.

Perimenopause, in four numbers

  • Seven days. A lasting swing of seven days or more in your cycle length is the clinical marker of early perimenopause.
  • Sixty days. A single gap of sixty days without a period marks the late stage.
  • Four to eight years. The usual length of the whole transition, which most often begins in the mid-forties and can begin in the mid-thirties.
  • Zero. The number of blood tests that can diagnose it.

Can a blood test diagnose perimenopause?

The hormone your doctor checked was almost certainly FSH. It climbs as the ovaries slow down, and after menopause it stays high, which makes it a reasonable way to confirm the end of the process.

During the transition it behaves nothing like that. Levels rise and fall from one week to the next, so the same woman can produce a menopausal reading in March and an entirely ordinary one in April without a single thing having changed. One blood draw captures one morning out of a process that runs for years.

The UK’s National Institute for Health and Care Excellence, which sets the clinical standard most English-speaking countries measure themselves against, is blunt about it. For women over 45, doctors are told not to order the test at all, and to make the diagnosis on symptoms and cycle pattern instead. Between 40 and 45 it is worth running twice, six weeks apart. Under 40 it becomes important for a different reason, because premature ovarian insufficiency has to be ruled out.

A normal result does not mean you are not in perimenopause. It means the test was taken on a day when it had nothing to show.

What actually stages perimenopause: the two dates

Clinicians worldwide stage this transition using a system called STRAW+10, agreed by an international workshop on reproductive ageing. It does not run on hormones at all. It runs on the dates in your calendar.

Stage What the calendar shows How long it runs
Early perimenopause Cycle length swings by seven days or more from your usual, so a 26-day month is followed by a 34-day one The longest stretch, and the most variable
Late perimenopause Two or more cycles skipped, or a single gap of sixty days One to three years
Menopause Twelve consecutive months with no period at all A single day, and you can only name it a year later

What counts is a change from your own normal, not a match to anyone else’s. If your cycle has always run to thirty-two days, you are not late. You are regular. The signal is the shift.

There is one caveat, and it applies to a great many women in their forties. The combined pill and the hormonal coil either flatten the bleed or remove it entirely, which takes the calendar out of play. If that is you, the record described further down carries the whole case on its own.

Which blood tests are worth asking for?

Two of them, and neither is a hormone.

The first is ferritin, which measures the iron you have in storage. Heavy, unpredictable bleeding is one of the earliest features of perimenopause, and it empties those stores quietly over months. Low ferritin produces exhaustion, breathlessness on the stairs, cold hands, hair in the shower drain and a slow, cotton-wool quality to your thinking. Every one of those gets filed under hormones and left there.

The second is a full thyroid panel. An underactive thyroid produces almost exactly the same picture, it is common in women in their forties, and it responds to treatment.

Both hold steady from one week to the next, and both hand you something you can act on this month.

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How to track perimenopause: three cycles, four lines a day

You do not need an app, a ring or a subscription. You need three months and four lines.

  1. The date your period starts, and the gap since the last one. This is the entry that stages you. Everything else is supporting material.
  2. How many days were heavy. Write the number down.
  3. The time you woke in the night. Just the time.
  4. One word for your mood, written at the same hour every day.

Keep a fifth line loosely, for anything that has changed and that you cannot account for. Two glasses of wine now costing you the whole of Sunday. A room that used to be comfortable and is now too warm. A knee. A name you could not retrieve in a meeting.

Ten minutes with a doctor goes a great deal further when you arrive holding dates rather than impressions.

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What to say at your appointment

Lead with the record rather than with an apology.

“I have tracked three cycles. My cycle length has moved from twenty-eight days to somewhere between twenty-four and thirty-six. I am waking between three and four most nights. I would like to talk about whether this is perimenopause, and I would like ferritin and a full thyroid panel.”

If you are over forty-five and an FSH test is offered, it is fair to ask what the result would change. If you are under forty-five, ask for it twice.

Then ask for the conversation to go into your notes. That single line is what makes the next appointment shorter than this one.

What to do while you wait for an appointment

Three things repay the effort whether or not perimenopause turns out to be the answer.

Eat protein and lift something heavy. Muscle and bone both start to go in this decade, and both respond to training rather than to a diagnosis. Protein at every meal, and two sessions a week with weight in your hands.

Repair sleep before you troubleshoot hormones. Broken nights produce most of what gets called brain fog. The bedroom temperature, the last drink of the evening and the phone on the nightstand are all considerably cheaper to change than an endocrine system.

Keep writing it down. Whatever you are told in month three, month twelve will tell you more.

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Start tonight

Open your phone and write down two dates: today’s, and the day your last period began. Add a line tomorrow.

In three months you will be holding something no blood test was ever going to give you.

Frequently asked questions

Can I track perimenopause if I am on the pill or have a hormonal coil?

Not by cycle length, because both suppress or remove the bleed. Track symptoms instead: night waking, mood, temperature, joint aches and sleep quality, dated the same way. Bring that record and say clearly which contraception you use, because it changes how your clinician reads everything else.

What age is too young to be taken seriously?

Perimenopause usually starts in the mid-forties and can begin in the mid-thirties. Symptoms before forty deserve a fuller work-up rather than reassurance, because premature ovarian insufficiency needs to be excluded. Being told you are too young is an observation about your age, not a diagnosis.

How long does perimenopause last?

Most women pass through it in four to eight years, though some take two and others take a decade. The late stage accounts for one to three of those years. Menopause is confirmed only after twelve consecutive months without a period, so the finish line is always named in hindsight.

Which symptoms should be seen sooner rather than later?

Bleeding heavily enough to soak through protection every hour, bleeding between periods, bleeding after sex, cycles arriving closer than twenty-one days apart, or any bleeding at all after twelve clear months. None of those are simply perimenopause and all of them warrant an appointment now rather than in three months.

Are the private hormone testing kits worth buying?

Most measure the same unstable hormone your doctor already measured, on a day you chose at random, and they carry the same limitation at a higher price. Money is better spent on ferritin and thyroid testing, which produce numbers that hold still and can be treated.

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Supplements support a plan. They do not replace one, they are not a substitute for a conversation about hormone therapy with a qualified clinician, and nothing here should delay that conversation.

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This article is for information and does not replace individual medical advice.