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.
