Irregular periods: common causes and when to see a doctor

Periods can shift around without anything being wrong — but a pattern of missed or unpredictable periods is worth understanding. Here's what can cause it, and when it's worth checking in with a doctor.

What causes irregular periods?

Irregular periods have many causes, including stress, weight changes, pregnancy, and hormonal changes due to polycystic ovaries or thyroid-related issues.

Other things that can affect your period negatively: sudden weight changes (gain or loss), excessive exercise, and medication — especially anti-emetics and blood pressure medicines.

Stress on its own can delay, alter, or even stop your periods. Both physical and emotional stress can play a role in your menstrual cycle.

Could a missed period mean I'm pregnant?

A missed period is the most common first sign of pregnancy. Do a home urine pregnancy test — if it's positive, see a doctor to confirm and begin your care.

If the test is negative, a late period can still have other explanations: stress, illness, hormonal problems, thyroid disorders, and sudden weight changes can all affect your cycle.

Is it normal for a period to just skip sometimes?

Your period can skip sometimes. But pregnancy and other causes must be ruled out if it's missed repeatedly, or for a longer duration.

Does birth control affect my periods?

Birth control pills can affect your periods — they make periods lighter, more regular, and less painful, and they can affect the number of bleeding days as well. (For how PCOS relates to fertility, see our PCOS and fertility guide.)

More questions our doctors have answered

Can breastfeeding make my cycles irregular?

Yes. During breastfeeding, as hormones fluctuate, you can experience irregular cycles, spotting, or absent periods. See a doctor if periods are absent along with nausea, weakness, or vomiting, or if you have heavy cycles or pain during menses.

When do periods return after delivery?

Normal periods usually return within 8 to 12 weeks after delivery if you're breastfeeding; with exclusive breastfeeding, periods may be absent, irregular, or delayed. See a doctor if you have heavy vaginal bleeding for 4 to 6 weeks after delivery, foul-smelling discharge, or persistent or severe lower abdominal pain.

Can I get pregnant again soon after delivery, even before my period returns?

Yes. Ovulation may occur even before a missed period — meaning there is a chance you might get pregnant before your period has told you anything at all. See a doctor if your period is missed for more than 8 to 12 weeks after delivery.

What causes spotting between periods?

The various causes include hormonal changes, infection, cervical or uterine conditions, pregnancy, and ovulation.