Question:
My girlfriend has gotten her period a week before she is supposed to and she is on the pill. She has had regular periods for three years. On a Web site, I saw it could be an STD or a pregnancy, or nothing. What is it, most likely? What should she do?

Answer:
Irregular bleeding while a woman is on the birth control pill is extremely common and is usually not indicative of anything being seriously wrong. Taking pills irregularly or missing pills are known to cause this problem frequently.

Much less frequently, it can be a sign of something more significant, like a sexually transmitted infection (STI) such as chlamydia.

Your girlfriend should call our Women's Health triage nurse at 863-2633. The nurse will take a thorough history related to her bleeding and will determine whether it calls for further evaluation.

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This column is not intended to replace advice from your personal clinician. If conditions persist, see a clinician.