What happened half a month earlier?

Menstruation ahead of half a month, refers to the two menstrual cycles, the middle and shows the symptoms of bleeding, the main reason may be the first, this bleeding is not the real menstruation, but a breakthrough bleeding ovulation period, the amount of bleeding and the usual menstruation compared, significantly reduced, bleeding time is also relatively short, in 3~5 days will be clean. Second, ovarian luteal dysfunction, premature atrophy, resulting in early endometrial exfoliation caused by the phenomenon of early menstruation. Third, taking emergency contraception, because of the role of emergency contraception withdrawal, caused by the symptoms of early menstruation.