Cycle
Why are my periods changing in perimenopause?
Quick answer
Changing periods are often the first sign of perimenopause. As ovulation becomes less regular and hormones fluctuate, cycles can get shorter, then longer, and bleeding can be heavier, lighter or less predictable, sometimes for several years. Many changes are expected, but some are not: very heavy bleeding, bleeding between periods or after sex, and any bleeding after a year without periods should always be checked. Tracking dates and flow shows which you are dealing with.
What might be happening
In early perimenopause, cycles often shorten by a few days, so periods seem to arrive more often. Later, ovulation is skipped in some months, and cycles stretch out with longer gaps or missed periods. These shifts can continue for several years before menopause, which is defined as 12 months without a period.
In cycles without ovulation, estrogen can build up the womb lining without the usual progesterone to balance it, so the bleed that follows can be heavier or longer. That is why some women have their heaviest periods in their 40s, even if they never did before.
NICE guidance uses irregular periods, together with symptoms such as hot flashes, to diagnose perimenopause in women over 45. Professional bodies also stress that perimenopause does not explain every change. Fibroids, polyps, thyroid problems and, less commonly, changes in the womb lining can also cause abnormal bleeding, so bleeding that breaks your usual pattern is worth having checked.
What to notice
- The first day of each period, so you can see cycle length.
- How many days you bleed, and your heaviest day.
- Flow: how often you change pads or tampons, flooding or large clots.
- Spotting or bleeding between periods, or after sex.
- Pain, and how PMS symptoms are changing.
- Tiredness, breathlessness or feeling faint during or after periods.
Three to six months of dates and flow notes shows whether changes follow a typical perimenopause pattern or something that needs looking at.
Related patterns
Women noticing their periods change in perimenopause often also notice:
- PMS feeling stronger or lasting longer
- sleep disruption around their period
- bloating that comes and goes
- mood and anxiety shifts with the cycle
- hot flashes or night sweats starting
- headaches or migraines changing pattern
When these shift at the same time as your cycle, it often helps to view them together rather than one by one.
Notice the pattern
Period changes in perimenopause are rarely a straight line. A run of short cycles can be followed by a long gap, then a heavy period, which makes it hard to know what is normal for you.
Dated notes on cycle length and flow cut through that uncertainty. They show a doctor exactly what has changed, and they make it easier to spot the bleeding patterns that should not be put down to perimenopause.
When to get support
Speak to a doctor if:
- your periods are heavy enough to affect daily life, or you are flooding or passing large clots
- you bleed between periods or after sex
- your periods come every two to three weeks for several months in a row
- you feel tired, breathless or faint, which can be signs of low iron
- you have any bleeding after 12 months without a period
If you are soaking through protection very quickly, or feel faint or very unwell, get urgent help from your local emergency services.