Menstrual Irregularity

Menstrual irregularity means periods that come too often, too rarely, at unpredictable times, or that stop. In adults, a typical cycle lasts 24 to 38 days. Some irregularity is normal in the first years after periods start and in the years before menopause. Common causes include pregnancy, polycystic ovary syndrome (PCOS), thyroid problems, high prolactin, weight changes, intense exercise, stress, breastfeeding, some contraceptives and medicines, primary ovarian insufficiency before age 40, and early menopause. Irregular cycles often mean ovulation isn't happening regularly, which can affect fertility.

Lab tests linked to menstrual irregularity:

• Progesterone (serum): rises after ovulation. A level measured about a week before an expected period helps show whether ovulation has happened.
• Doctors usually start with a pregnancy test (hCG), TSH and prolactin. They may add FSH, LH and estradiol, testosterone and SHBG when PCOS is suspected, and a pelvic ultrasound.

How results are read:

• A mid-luteal progesterone above about 3 ng/mL usually suggests ovulation has happened. Timing matters, so a low result in an irregular cycle may just mean the test was done on the wrong day.
• A raised TSH or prolactin points to a thyroid or pituitary cause.
• A high FSH on repeat testing in someone under 40 suggests primary ovarian insufficiency.
• Raised testosterone with irregular periods, with or without polycystic ovaries on ultrasound, can point to PCOS once other causes are ruled out.

When to see a doctor:

• See a doctor if periods stop for 3 months, bleeding happens between periods or after sex, or your cycle pattern changes and stays changed. In adults, cycles that are repeatedly shorter than 24 days or longer than 38 days are worth discussing. In teenagers, cycles of 21 to 45 days are common.
• See a doctor about very heavy periods, especially with tiredness or breathlessness.
• Get emergency care for heavy bleeding that soaks a pad or tampon every hour for several hours, or severe abdominal pain with a positive pregnancy test.

Clinical takeaway: menstrual irregularity is assessed with a pregnancy test, TSH, prolactin and other hormones, and a well-timed progesterone shows whether ovulation is happening.