By Sophora Editorial · Evidence reviewed · Published July 2026 · Last reviewed July 2026
Your period used to be reliable. It may not have arrived on exactly the same day every month or always come without symptoms, but it was broadly predictable in a way your body had settled into.
Now it seems to arrive on its own schedule. Sometimes early, sometimes two weeks late, sometimes heavier than it has been in years, sometimes barely there.
You might go three months without one and then bleed twice within a few weeks. You are tracking it and cannot find the old rhythm anymore. Perimenopause may be the reason, but new bleeding changes still deserve attention because hormones are not the only possible cause.
Changes in cycle timing and flow are common during perimenopause and may be among its earliest signs. Understanding what is driving those changes can make the pattern less confusing while helping you recognise when bleeding needs medical assessment.
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What is actually happening to your cycle
A regular menstrual cycle depends on an ongoing conversation between the brain, the pituitary gland, and the ovaries.
Clinicians call this the hypothalamic-pituitary-ovarian axis, or HPO axis. During the reproductive years, the conversation usually follows a familiar sequence: the pituitary releases FSH, a follicle develops and produces estrogen, an LH surge helps trigger ovulation, and the structure left behind after ovulation produces progesterone.
If pregnancy does not occur, hormone levels fall, the uterine lining sheds, and the conversation starts again.
During perimenopause, this conversation becomes less predictable. As the number of available ovarian follicles declines, one of the signals that normally helps regulate FSH, called inhibin B, also falls.
The brain may respond by sending a stronger FSH signal to encourage the ovaries to act. Some months, they respond and ovulation happens.
Other months, the process stalls or ovulation does not happen at all. The result can be a perfectly ordinary-looking cycle followed by one that is unusually short, unexpectedly long, or missing altogether.
Hormone levels can also change substantially from one cycle to the next, which is why one blood test is often more of a snapshot than the whole film.
This is where the two most characteristic period changes of perimenopause come from.
When ovulation is skipped (anovulation): the structure that normally forms after ovulation, called the corpus luteum, does not develop. That means the usual rise in progesterone does not happen.
Estrogen may continue acting on the uterine lining without progesterone providing its usual balancing effect. The lining can then shed on a less predictable timetable: after a long gap, over many days, or as unexpectedly heavy bleeding. In other words, the calendar may look chaotic, but there is biology behind the chaos.
This is one mechanism behind perimenopausal bleeding changes, although fibroids, polyps, medicines, and other medical conditions can produce similar symptoms.
When hormone levels fluctuate unpredictably: estrogen can be high in one cycle and lower in the next, while the amount of progesterone depends largely on whether ovulation occurred.
Those shifts affect both when bleeding happens and how much uterine lining, or endometrium, is available to shed. Some women experience sudden heavy flow or flooding. Others have lighter periods, spotting, or long stretches of nothing followed by an inconvenient surprise.
Heavy bleeding should not automatically be blamed on perimenopause, however, because fibroids, polyps, adenomyosis, pregnancy-related causes, medicines, bleeding disorders, and endometrial disease can also change bleeding patterns.
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What perimenopause period changes actually look like
Cycles getting shorter first
One of the earliest signs of perimenopause, often noticed in the late 30s or early 40s. The follicular phase can shorten as reproductive ageing changes follicle recruitment and hormonal feedback, bringing periods slightly closer together. A cycle that was 28 days may become 24 or 25 days.
Cycles getting longer and then skipped
As perimenopause progresses and anovulatory cycles become more frequent, cycles lengthen. A 28-day cycle may stretch to 35, 45, or 60 days. Skipped periods become more common. A skipped period can occur in perimenopause, but pregnancy should still be considered when it is possible, and irregular cycles do not mean pregnancy is impossible.
Heavier and longer periods
Particularly common in late perimenopause. Anovulatory cycles can expose the uterine lining to estrogen without the usual cyclic progesterone effect, contributing to irregular, prolonged, or heavy bleeding. Some women experience flooding for the first time in their 40s, but new heavy bleeding still warrants clinical assessment rather than being assumed to be hormonal.
Lighter periods or spotting
Some periods become lighter as hormone production and endometrial development vary from cycle to cycle. Brown discharge may represent older blood leaving the uterus. Spotting can occur during the menopausal transition, but persistent bleeding between periods should be assessed because hormonal fluctuation is only one possible cause.
Two periods close together
A long bleed followed within a few weeks by another episode, or two bleeding episodes in one calendar month, can occur during perimenopause. The pattern may reflect variable cycle length or irregular endometrial shedding, but frequent or persistent bleeding should be discussed with a clinician.
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What is within the range of perimenopause and what needs investigating
Many period changes occur as part of the menopausal transition, but bleeding changes should still be discussed with a clinician, especially when they are heavy, prolonged, frequent, persistent between periods, occur after sex, or appear after menopause. Symptoms alone cannot reliably identify the cause.
See a doctor promptly if:
- You are soaking through a pad or tampon every hour for two or more consecutive hours
- Your period lasts longer than seven days
- You are passing blood clots larger than a 50p coin or a quarter
- You have bleeding or spotting between periods that is persistent rather than occasional
- You have bleeding after sex
- You have any bleeding after twelve consecutive months without a period (this is postmenopausal bleeding and always needs assessment)
- Heavy bleeding is accompanied by dizziness, breathlessness, or significant fatigue, which may indicate anaemia
- Your cycle changes are accompanied by significant pelvic pain
Heavy bleeding during perimenopause can be related to ovulatory dysfunction, but fibroids, adenomyosis, endometrial polyps, medicines, pregnancy-related causes, bleeding disorders, and endometrial hyperplasia or cancer are among the other possibilities.
Assessment may include a pregnancy test when relevant, blood tests such as a full blood count, pelvic examination, ultrasound, hysteroscopy, or endometrial sampling depending on your age, symptoms, risk factors, and local clinical guidance.
One thing many women do not realise: you can still get pregnant
Irregular periods in perimenopause do not mean ovulation has stopped. Anovulatory cycles and ovulatory cycles can alternate unpredictably.
You can ovulate in months where your period appears to have skipped, or in months where the cycle is very long. Pregnancy in perimenopause is less common but not impossible, and it can come as a significant surprise.
If you are not using hormonal contraception, UK guidance advises continuing contraception for one year after the final natural period if you are 50 or older, and for two years if you are under 50. Hormonal contraception can alter or stop bleeding, so the timing of menopause may be harder to judge while using it.
Some hormonal methods can also reduce heavy bleeding. The choice depends on age, medical history, contraception needs, and individual risk factors, so it is worth discussing with a clinician.
What helps
Track the picture, not just the dates. Start recording cycle length, flow volume (light, moderate, heavy, flooding), how many days the period lasts, and any spotting between periods. A few months of this data is far more useful in a clinical appointment than a vague description of things being unpredictable. Sophora’s Today’s Check-in tracks this alongside your other symptoms so the picture builds automatically.
For heavy bleeding: tranexamic acid is a non-hormonal treatment that can reduce menstrual blood loss substantially and is generally taken only during bleeding, according to the prescribed regimen. NSAIDs can also reduce menstrual blood loss and period pain for some people.
These medicines are not suitable for everyone, so treatment should be chosen with a clinician or pharmacist who can check contraindications, interactions, and the cause of the bleeding.
For bleeding control and contraception together: hormonal options may include a levonorgestrel-releasing intrauterine system, combined hormonal contraception, or selected progestogen regimens. They do not all affect bleeding in the same way, and suitability varies with age, migraine history, smoking, blood-pressure and clotting risk, other medical conditions, and personal preference.
For other perimenopause symptoms: HRT can treat symptoms such as hot flushes and night sweats, but it is not a contraceptive and should not be presented as a treatment for unexplained heavy or irregular bleeding.
The HRT regimen used during perimenopause can itself produce scheduled or unscheduled bleeding. Bleeding should be assessed appropriately before treatment decisions are made, and the regimen should be reviewed if unexpected bleeding persists.
Check for anaemia. Sustained heavy bleeding can cause iron deficiency and iron-deficiency anaemia. Fatigue, breathlessness, palpitations, dizziness, or reduced exercise tolerance alongside heavy bleeding deserve medical attention. A full blood count is commonly used to check for anaemia; further iron studies may be appropriate. Iron treatment should be based on clinical assessment and the relevant test results.
“The unpredictability has a biological explanation: ovulation and hormone production become less consistent during the menopausal transition. Understanding the mechanism does not make heavy bleeding easier to manage, but it can help you describe the pattern clearly and know when to seek assessment.”
Preparing for the appointment
Use Sophora’s The Answers You Need before your appointment. It builds a doctor-ready summary from four questions, to bring your tracking data, your specific symptoms, and the right questions to your appointment. Irregular periods in perimenopause are common enough that doctors may underestimate their impact on daily life.
Having the data ready, specifically cycle length variability, flow volume, and the frequency of flooding or spotting, ensures the clinical picture is taken seriously and investigated appropriately.
Questions you are probably asking
How do I know if my irregular periods are perimenopause or something else?
Age, menstrual history, symptoms, pregnancy possibility, medicines, and other health factors all matter. In otherwise healthy people aged 45 or over with typical symptoms, perimenopause is usually diagnosed clinically rather than with routine hormone tests.
Irregular bleeding can also have other causes, including pregnancy, thyroid disorders, polycystic ovary syndrome, fibroids, polyps, medicines, and endometrial conditions. Under 45, and especially under 40, earlier menopause or premature ovarian insufficiency requires a different diagnostic approach. FSH testing is used selectively rather than as a routine single test for everyone in perimenopause.
My periods have always been regular. Why are they suddenly so unpredictable?
Because reproductive ageing changes the conversation between the ovaries, pituitary gland, and brain. Follicle development, ovulation, and estrogen and progesterone patterns become more variable, so a cycle that behaved predictably for decades can begin to shorten, lengthen, skip, or change in flow.
Your body has not forgotten how calendars work; the hormonal signals controlling the cycle are becoming less consistent. The transition is not identical for everyone, and a sudden or concerning bleeding change should still be assessed rather than assumed to be perimenopause.
Is a missed period in my 40s definitely perimenopause?
A missed period in your 40s can be part of perimenopause, but it is not specific to it. Pregnancy should be considered first when possible. Thyroid disorders, major changes in weight or energy balance, some medicines, stress, and other reproductive conditions can also alter cycles.
In people aged 45 or over with typical symptoms, diagnosis is usually based on age, symptoms, and menstrual history rather than routine hormone testing.
How long do irregular periods last in perimenopause?
The duration varies widely. Perimenopause often lasts several years; commonly cited estimates place the average at about four years, although the transition can be shorter or longer.
Cycle changes do not always progress in a straight line. Menopause is identified retrospectively after 12 consecutive months without a menstrual period when there is no other cause and hormonal contraception is not masking the bleeding pattern.
In summary
You now know: During perimenopause, reproductive ageing makes follicle recruitment, ovulation, and ovarian hormone production more variable. Anovulatory cycles lack the usual post-ovulation progesterone rise and can contribute to irregular, prolonged, or heavy bleeding. Hormonal change is common, but it is not the only possible cause of a new bleeding pattern.
One thing to do: Start tracking now if you are not already. Cycle length, flow volume, duration, and any spotting. Three months of this data changes a medical appointment from a vague conversation about things being irregular to a specific, clinically useful picture.
Hold onto this: Irregular does not mean unmanageable. Perimenopause can explain major cycle changes, and effective treatments for heavy bleeding are available. Tracking gives you evidence; assessment helps identify the cause; treatment can then be matched to the problem rather than guessed.
Track this. Understand it. Bring it to your appointment.
Sophora tracks your cycle changes alongside everything else your body is doing, so the picture builds automatically.
Today’s Check-in inside Sophora logs cycle length, flow, and symptoms in one place. The Symptom Decoder connects your period changes to your wider hormonal picture. The Answers You Need turns your tracked data into a clinical summary you can bring to any appointment so the conversation is specific rather than vague.
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References
- American College of Obstetricians and Gynecologists (ACOG). Perimenopausal Bleeding and Bleeding After Menopause.
- American College of Obstetricians and Gynecologists (ACOG). Abnormal Uterine Bleeding.
- National Institute for Health and Care Excellence (NICE). Menopause: identification and management. NG23. Updated guidance.
- National Institute for Health and Care Excellence (NICE). Quality Standard QS143: Diagnosing perimenopause and menopause.
- NHS. Symptoms of menopause and perimenopause. Guidance on contraception after the final menstrual period.
- Mayo Clinic. Perimenopause: Symptoms and causes. Updated clinical overview.
- Cochrane. Antifibrinolytics, including tranexamic acid, for heavy menstrual bleeding. Evidence review.
- Cochrane. Non-steroidal anti-inflammatory drugs for heavy menstrual bleeding. Evidence review.
Last reviewed: July 2026 · Review due: October 2026 · Not therapy. Not medical advice. For your own use and understanding only. · mysophora.com