Periods Every 2 or 3 Weeks in Your 40s: When Shorter Cycles Are Normal

If your period now shows up every 19 to 23 days instead of every 28, you may be at the very start of the years before menopause. The international staging system for reproductive aging, known as STRAW+10, lists shorter cycles as the first change, in the late reproductive stage.¹ The NHS² agrees that one of the first signs of perimenopause is usually a change in periods, which “may happen more often or less often.”²

Where shorter cycles fit

Stage (STRAW+10)	What your cycles do
Late reproductive	Subtle changes begin, specifically shorter cycles1
Early transition	Lengths start to swing: a difference of 7 days or more between back-to-back cycles that happens again within 10 cycles1
Late transition	A stretch of 60 days or more with no period; this stage lasts 1 to 3 years on average1
After menopause	No period for 12 months; any bleeding after that needs a check2

Cycles don’t move in a straight line. In a five-year study of 156 women aged 25 to 58 who recorded every bleed, cycle length became more variable with age, and most women’s average cycle got longer during their 40s.³ The researchers also found that a woman’s cycle lengths varied too much to predict her hormone levels.³ One short cycle tells you little; a run of them tells you more.

How short is too short?

• ACOG⁴ counts cycles shorter than 21 days as abnormal uterine bleeding, along with cycles longer than 35 days and cycles that vary by more than 7 to 9 days.⁴
• ACOG⁴ also says the days between periods may change in perimenopause, and that you should still talk with an ob-gyn about abnormal bleeding even when the change is expected.⁴
• Count from day one to day one: the first day of one period to the first day of the next. Our cycle length calendar does the counting.
• Is it a period, or spotting between periods? Light bleeding that isn’t a full period counts as bleeding between periods, which is on ACOG’s⁴ list too. See why you’re spotting between periods.

Why it’s worth a visit

ACOG⁴ lists the usual causes of bleeding changes at this age:

• Skipped ovulation. Without ovulation for several cycles, the uterine lining can grow too thick. This happens in perimenopause, and also with PCOS and an underactive thyroid.⁴
• Fibroids and polyps, noncancerous growths that can cause irregular or heavy bleeding.⁴
• Adenomyosis, where the lining grows into the muscle wall of the uterus.⁴

Your clinician may suggest a pelvic ultrasound or an endometrial biopsy. Bring dates, not adjectives: see five records for a heavy period visit and what a normal cycle looks like.

Try: “My cycles were 28 days for years. The last five started 20, 22, 19, 23 and 21 days apart. Is this perimenopause, and do I need any tests?”

Period, Handled covers this in Chapter 9, “Off Schedule.” Its Period Scorecard asks you to write down the start date of every period, even a light or short one, and to log spotting days separately, because the STRAW+10 markers run on cycle length. The chapter’s visit script opens with those numbers. See the book.