Teen Menstruation: Irregular Periods
For the first two years after girls start their periods, it is very common for them to be irregular. But after a few years of regular periods, you should be concerned if they suddenly become irregular. In that case, I recommend your daughter be evaluated by a physician.
While pregnancy is the most common reason women stop having periods, there are other reasons as well. Thyroid disease, polycystic ovarian syndrome, rigorous regular exercise and eating disorders are a few of the other possible causes. A gynecologist can sort out these issues for you.