Do girl's periods become sporadic after they first start having sex?

(sparatic -> sporadic?)

‘only if they’re pregnant’ is my smartass remark. Extremely low body fat will stop menstruation, illness and ,of course, being pregnant. I was erratic when in my teens.

Sexual activity should make no difference, other than the initial breaking of a female’s hymen, or as faye mentioned…pregnancy. If you, or the person you are speaking for, hasn’t been to a gynecologist, it’s time for a visit. It will put the person at ease to find out that they are fine and/or be offered a solution, should there be a problem.

And please use protection at all times while having sex. Having a baby at this point in your life is probably something you have not planned for.

Did you mean sporadic? Sex has no effect on periods except that they stop when you are pregnant.

Sex doesn’t affect periods, except if one become pregnant. duh.
BUT, sex can lead to stress, weight loss, and other things that can and usually WILL affect periods. After i began having sex, my periods were no different than before. I always had periods that weren’t on a normal schedule. Birth control came in to regulate.

If you don’t use protection, they’ll be about 9 months apart.

I don’t know anything about the girl you’re concerned about but it’s pretty normal for periods to be a bit irregular for the first couple years of them. Mine were never clockwork until I went on birth control. This of course doesn’t have anything to do with sex and doesn’t get you off the hook sexually. You’ve still gotta use protection.