Irregular periods in perimenopause

What counts as an irregular cycle

A cycle is counted from the first day of one period to the day before the next one starts. The NHS puts the average at around 28 days and calls periods irregular when the gap is shorter than 21 days or longer than 35. The American College of Obstetricians and Gynecologists (ACOG) gives a slightly wider normal range, 24 to 38 days, with the bleed itself lasting up to 8 days.

The two bodies draw the line in slightly different places, so a single 36-day cycle is no cause for alarm. What tells you more is your own pattern. If your cycles held within two or three days of each other for years and now swing by a week or more, that change is the thing to notice, even when every cycle still falls inside the normal range.

Why cycles change in perimenopause

ACOG explains that in perimenopause the ovaries make less estrogen, and they no longer release an egg every month. Some months they do, other months they do not. Because ovulation is what sets the timing of the next period, a cycle without it can run long, end early or bring a different amount of bleeding. ACOG sums up the result for women in their 40s plainly: periods may be shorter or longer, the days between them may increase or decrease, bleeding may get heavier or lighter, and you may skip periods.

The NHS lists nearing menopause, usually between 45 and 55, as one of the most common reasons for irregular periods, alongside puberty. It also says irregular periods are not usually a sign of a problem, and still advises speaking to a GP when your usual pattern changes.

Periods closer together: often the first change

Many women expect perimenopause to mean fewer periods, so periods arriving every three weeks can come as a surprise. Shorter cycles are in fact one of the earliest signs. The STRAW+10 staging system, the framework researchers and clinicians use to describe reproductive ageing, notes that subtle changes in the cycle, specifically shorter cycles, begin in the late reproductive years, before the menopausal transition is said to have started.

STRAW+10 then marks the start of the early menopausal transition by variability: a difference of at least 7 days between the lengths of consecutive cycles, which happens again within the next 10 cycles. In practice that might look like a 23-day cycle followed by a 31-day one, then a few ordinary months, then another swing. One odd month on its own does not meet that definition. A repeated swing does.

When the change shows up as a period at both ends of the same month, our guide to two periods in one month explains why the first half of the cycle shortens in your 40s and when cycles under 21 days need a doctor.

Longer periods in perimenopause: is it normal?

Longer bleeds are common as you get closer to your last period. A review of menstrual changes before the final period, by the epidemiologist who led the STRAW+10 bleeding work, describes a high probability of episodes of excessive and prolonged bleeding in this stage.

That they are common does not mean you should ignore them. ACOG's list of bleeding that is not normal includes bleeding that is heavier or lasts for more days than usual, and the NHS advises seeing a GP if periods last longer than 7 days. So if your periods used to last five days and now last nine, that belongs in the conversation with your doctor, even if a friend tells you hers did the same. When the longer periods are also heavier, with flooding or large clots, our guide to heavy periods and blood clots in perimenopause sets out the measurable signs.

Missed periods and long gaps

Skipped periods usually come later. STRAW+10 marks the late menopausal transition by a gap of at least 60 days with no period, and estimates that this stage lasts 1 to 3 years on average. Cycles in this stage keep varying in length, and ovulation becomes less frequent. Hot flashes and night sweats are likely to appear around now as well. Where these stages fall by age, and how long the whole transition runs, is covered in when perimenopause starts.

A missed period in your 40s is not automatically perimenopause. The NHS points out that a missed period is often an early sign of pregnancy, and the review above notes that ovulation can still happen right up to the final period. If there is any chance you could be pregnant, a pregnancy test is the first step. The NHS advises using contraception until 2 years after your last period if you are 40 to 49, and for 1 year after it if you are 50 or over.

A gap only counts toward menopause once it reaches 12 months. ACOG defines menopause as a full year with no periods, with an average age of 51 in the United States. A period that turns up at month 10 resets the count. Any bleeding after those 12 months, however light, is a reason to see your doctor.

Other causes of irregular periods

Perimenopause is the most likely reason in your mid-40s, but it shares the symptom with several other things. The NHS lists:

• pregnancy
• hormonal contraception, including the progestogen-only pill, the contraceptive injection and the hormonal coil
• losing or gaining a lot of weight
• stress and anxiety, and exercising too much
• thyroid problems (see perimenopause or thyroid?), and polycystic ovary syndrome (PCOS)

Hormonal contraception deserves a second mention, because it can mask the changes completely. If your bleeding is controlled by a coil or a pill, your periods may tell you very little about where you are in the transition, and the other symptoms become the more useful record.

ACOG adds causes found inside the womb, such as polyps and endometrial hyperplasia, a thickening of the lining that is not cancer but can lead to it in some cases. These are part of why a doctor wants to hear about a change in bleeding rather than have you wait it out.

Which changes to report, and how soon

ACOG's advice is to talk with your doctor about bleeding changes in perimenopause, even though changes are expected. Some are more pressing than others. I would book an appointment, without waiting for the next routine one, for any of these:

• bleeding or spotting between periods (our guide to spotting between periods in perimenopause covers its causes and how soon to go)
• bleeding or spotting after sex
• periods lasting longer than 7 days, or longer than is usual for you
• bleeding heavier than usual, or heavy enough to soak a pad or tampon every hour or two
• irregular periods together with tiredness, weight gain, new facial hair, or dry or oily skin, which the NHS singles out
• any bleeding after 12 months without a period

Cycles that come a few days earlier or later than they used to, with bleeding that is otherwise ordinary, can wait for a planned appointment. Mention them there, because the pattern helps your doctor place you in the transition. For women over 45, the NICE guideline on menopause says perimenopause is usually recognised from symptoms and cycle changes without blood tests, so your notes on your cycle carry real weight in that conversation. Our overview of perimenopause symptoms and how to track them sets the cycle changes beside everything else that can shift in these years.

How to track cycle length

The NHS suggests an app or a diary to see whether your periods are irregular. Memory is unreliable here, because a 25-day cycle and a 32-day one both feel like "about a month". For each period, write down:

• the date bleeding started, which is day 1
• the date it stopped, so you know how many days it lasted
• the flow on each day: spotting, light, medium or heavy
• any spotting or bleeding between periods, and any after sex

From the start dates you can work out each cycle length by counting the days from one day 1 to the next. Two numbers are worth flagging next to the list: any cycle that differs from the one before by 7 days or more, and any stretch of two months without a period. Those are the two markers STRAW+10 uses, and a doctor can read them at a glance.

Our printable symptom diary and appointment checklist has rows for flow and spotting beside your other symptoms, and you can take it to the appointment on paper. Six months of start dates is enough to show a trend, though three already tells a doctor more than "my periods are all over the place".

My take

I would start tracking start dates the first month a period surprises you, early or late, rather than waiting to see whether it happens again. Periods coming closer together in your early to mid-40s are an ordinary early sign. I'd still mention them at your next appointment, but longer periods, bleeding between periods and bleeding after sex are worth a call to the surgery that week. If periods stop for a couple of months, take a pregnancy test before assuming it is perimenopause. A short list of dates with the 7-day swings and the 60-day gaps marked will answer most of what your doctor asks first.

Related reading

Every piece on cycle and bleeding changes is collected under periods and bleeding, and the tracking and appointments topic covers how to keep a record a doctor can use.