Why do periods become irregular?
During perimenopause the ovaries make less estrogen, and ovulation stops being monthly. In a month with no egg released, the usual hormone sequence of the cycle doesn't happen, so the next period can come late, early, light or heavy.[1][2]
Changes usually start in the mid-40s, according to ACOG, and the timing varies from person to person.[1]
How cycles change, stage by stage
The stages of the menopause transition are marked by cycle length, and The Menopause Society describes them this way.[2]
At first the changes are small: cycles a little shorter than usual, more or fewer days of bleeding. As perimenopause goes on, cycle length can vary by 7 days or more. In the late stage, you can go 60 days or more with no period.[2] Your final period is only known in hindsight: menopause means a full year with no period.[1]
What counts as irregular?
| Measure | Typical range | Worth noting in perimenopause |
|---|---|---|
| Cycle length (day 1 to the next day 1) | 24 to 38 days | Shorter than 21 days, or a gap of 60 days or more |
| Change from one cycle to the next | Fairly consistent | 7 days or more, again and again |
| Days of bleeding | Up to 8 | More days than you usually have |
| Flow | Similar month to month | Much heavier, or flooding through protection |
The typical ranges are ACOG's, and the 21-day line is the NHS's definition of an irregular cycle.[1][3]
Which changes need a doctor?
ACOG says it's normal for periods to change near menopause, and still advises talking to an OB-GYN about bleeding changes. These ones it lists as not normal:[1]
- bleeding or spotting between periods
- bleeding or spotting after sex
- heavy bleeding during your period
- bleeding that is heavier or lasts more days than usual
- any bleeding after menopause
Polyps (noncancerous growths) and a thickened lining of the uterus are among the causes ACOG lists.[1] Very heavy periods can also leave you tired or short of breath a lot, and a doctor may do a blood test for iron deficiency anemia.[4]
A late period can also be pregnancy. You can still get pregnant in perimenopause, and the NHS advises contraception until 1 year after your final period if you're 50 or over, or 2 years if you're 40 to 49.[5] If you could be pregnant, a home test answers it.
How to measure your own cycle
Day 1 is the first day of your period, and the cycle runs to the day before the next one starts.[3]
- Write down the first day of every period, and the last day.
- Note the flow on each day: light, medium or heavy, and any spotting in between.
- After 3 periods, list the cycle lengths side by side.
Her Good Days counts the days for you. Once your cycle lengths vary, the period estimate becomes a wider range and the app says so, and the doctor report lists every period date with the cycle length between them. The free period and ovulation estimator works the same way in your browser, with the same caveat for irregular cycles.
For the other early signs, see the perimenopause symptoms checklist, and for this stage as a whole, perimenopause in Her Good Days.