Irregular periods
For most adults, a period comes every 24 to 38 days, and the gap from one cycle to the next varies by no more than about a week. Outside that range, the usual cause is irregular ovulation.
What counts as irregular
- Periods closer than 24 days apart
- Periods more than 38 days apart, or skipped for months
- Cycle lengths that vary by more than about 7 to 9 days from month to month
Cycles are often irregular in the first few years after a first period and in the years leading up to menopause.
Why it happens
When you do not ovulate, your body does not make progesterone, the hormone that stabilizes the uterine lining and triggers an orderly period. The lining keeps building and then sheds unpredictably. Common reasons include polycystic ovary syndrome (PCOS), thyroid disease, a high prolactin level, perimenopause, significant weight change, intense exercise, not eating enough, and stress. Pregnancy is always on the list.
Why it matters
Beyond the inconvenience, months without ovulation expose the lining to estrogen without progesterone. Over time that raises the risk of endometrial hyperplasia. Treatment protects the lining and makes bleeding predictable. It also helps if you want to become pregnant.
What evaluation usually involves
Expect a pregnancy test, thyroid and prolactin tests, and hormone tests if PCOS is suspected. A pelvic ultrasound is often part of it. People 45 and older, and younger people with long-standing irregular cycles and risk factors, may need an endometrial biopsy.
Sources
- Munro MG, Critchley HOD, Fraser IS; FIGO Menstrual Disorders Committee. The two FIGO systems for normal and abnormal uterine bleeding symptoms and classification of causes of abnormal uterine bleeding in the reproductive years: 2018 revisions. Int J Gynaecol Obstet. 2018;143(3):393–408.
- American College of Obstetricians and Gynecologists. Practice Bulletin No. 136: Management of abnormal uterine bleeding associated with ovulatory dysfunction. Obstet Gynecol. 2013;122(1):176–185 (reaffirmed).