For many people the first sign of perimenopause is not a hot flash. It is a period that arrives a week early, then one that does not arrive at all, then one so heavy it ruins a pair of trousers at work.
Cycle changes are among the most common and earliest signs of the menopause transition, and they are also one of the most confusing, because "irregular" covers everything from completely expected to needs checking this week. This guide explains what is happening, which patterns are typical, and which bleeding should go to a doctor rather than a wait and see.
This is general information, not medical advice. If something about your bleeding worries you, a doctor or gynaecologist is the right person to ask.
Why Periods Change in Perimenopause
A regular cycle depends on the ovaries releasing an egg on a fairly predictable schedule, with oestrogen and progesterone rising and falling in a steady pattern. In perimenopause, that pattern starts to break down:
- Ovulation becomes irregular. Some cycles release an egg, some do not. Cycles without ovulation (anovulatory cycles) produce little or no progesterone.
- Oestrogen swings more, not just less. Levels can be higher than usual in some cycles and low in others. It is not a smooth decline.
- The lining of the uterus responds to that. Oestrogen builds the lining, and progesterone stabilises it. When oestrogen runs high without enough progesterone, the lining can build up more than usual, which can lead to heavier or longer bleeding when it sheds.
That is why the same person can have a short light period one month and a long heavy one the next. Our guide on the signs and stages of perimenopause covers the transition as a whole.
What Typical Perimenopause Period Changes Look Like
Researchers usually describe the menopause transition in stages based on cycle changes. A widely used system (STRAW+10) describes it roughly like this:
| Stage | What cycles tend to do |
|---|---|
| Late reproductive years | Cycles still regular, but often slightly shorter, and flow may change |
| Early menopause transition | Cycle length varies more. A persistent difference of 7 days or more between consecutive cycles is a common marker |
| Late menopause transition | Gaps of 60 days or more between periods start to appear |
| Menopause | Confirmed after 12 months in a row with no period |
In practice, common patterns include:
- Shorter cycles early on, for example every 21 to 24 days instead of 28.
- Longer cycles later, with periods 40, 60 or 90 days apart.
- Skipped periods, sometimes followed by a period that is heavier than usual.
- Changes in flow, both heavier and lighter than you are used to.
- More or different premenstrual symptoms, such as breast tenderness, bloating or mood changes.
How long this lasts varies a lot. Perimenopause commonly runs for around four years, but it can be much shorter or longer than that.
Heavy Periods: Common, but Not Something to Just Put Up With
Heavy bleeding is one of the most underreported parts of perimenopause. People often assume it is just part of getting older and live with it for years. It is common, but it is also treatable, and it can cause real problems.
Signs that bleeding is heavier than it should be:
- Soaking through a pad or tampon every hour or two, for several hours in a row
- Needing to double up protection or change it during the night
- Passing clots larger than about a quarter (around 2.5 cm)
- A period lasting more than seven days
- Planning your day around being near a toilet
Ongoing heavy bleeding can lead to **iron deficiency and anaemia,** which causes tiredness, breathlessness, headaches, feeling cold and difficulty concentrating. Several of those overlap with other perimenopause symptoms, so it is easy to miss. A simple blood test can check your iron levels. If you have been putting fatigue down to perimenopause brain fog, it is worth asking about.
Treatment options exist and a doctor can talk you through which fit your situation. They include hormonal options, such as a hormonal IUD, and non hormonal medicines that reduce blood loss during a period. Some people find that HRT also changes their bleeding pattern, which is worth discussing in the same appointment.
When Irregular Bleeding Needs a Doctor
Not every change is just hormones. Fibroids, polyps, thyroid problems, pregnancy, and less commonly changes in the lining of the uterus (including, rarely, cancer) can all cause irregular bleeding, and they become more common with age. These are reasons to see a doctor rather than wait:
- Bleeding between periods
- Bleeding after sex
- Periods closer together than 21 days, consistently
- Periods lasting more than seven days
- Very heavy bleeding as described above, or feeling dizzy, faint or exhausted
- A sudden change in your pattern that does not settle
- Any bleeding after 12 months with no period at all. This is postmenopausal bleeding and should always be checked, even if it is light or only happens once
Most of the time the cause turns out to be benign. The point of checking is to make sure, and to get treatment if it is needed.
You Can Still Get Pregnant
Irregular periods do not mean you cannot conceive. Ovulation becomes less predictable, not absent, and a late period in your 40s can still be a pregnancy. If you do not want to get pregnant, keep using contraception through perimenopause. Common guidance, such as from the NHS, is to continue until you have had no period for 12 months if you are over 50, or for two years if you are under 50. Your doctor can tell you what applies to you, especially if you are using hormonal contraception that changes your bleeding anyway.
How to Track Perimenopause Periods Usefully
Standard period apps are built around predicting your next period, which is exactly what stops working in perimenopause. A prediction based on an average cycle becomes noise once cycles vary by weeks. What helps instead is a plain, honest record:
- Start and end date of each bleed, including spotting
- Flow, using a simple scale (light, medium, heavy, very heavy) and noting clots or double protection
- Other symptoms on the same days, such as hot flashes, poor sleep or mood changes
- Any medication or HRT, with the start date and dose
After three to six months this gives you a pattern you can actually describe. "My periods are irregular" is hard for a doctor to act on. "The last five cycles were 19, 34, 22, 61 and 25 days, and two of them were heavy with clots" is not.
Where Alva Fits
Alva is the perimenopause tracker we build for iPhone. It is designed for irregular cycles: you log each bleed, its flow and your symptoms, and it does not try to predict your next period from an average that no longer applies. If you start HRT, it keeps a dose history alongside your cycle log, and you can export a PDF summary to take to an appointment.
To be clear about the limits: Alva cannot tell you whether a bleeding pattern is normal for you or diagnose anything. If anything in the doctor list above applies, book the appointment. What Alva does is make sure you arrive with months of clear data instead of a rough memory.
The Short Version
- Irregular periods are one of the earliest and most common signs of perimenopause.
- Cycles often get shorter first, then longer, with skipped periods and changes in flow.
- Heavy bleeding is common but treatable, and can cause iron deficiency. Do not just put up with it.
- See a doctor for bleeding between periods, after sex, very heavy or very long periods, or any bleeding after 12 months with none.
- You can still get pregnant until menopause, so keep contraception going if you need it.
- Track dates, flow and symptoms rather than relying on period predictions.