Most hormonal birth control contain synthetic versions of the hormones estrogen and progesterone. By altering your hormone levels, birth control stops ovulation, changes the quality of your cervical mucus, and thins your uterine lining which makes implantation difficult. After you have taken birth control for a while your lining may become thinner, your period may become lighter, or you may stop having a period altogether. Some birth control methods will keep you from having a period, or will reduce the frequency of your menstrual cycles. Moreover, during the first few cycles on birth control, your menstrual cycle may take a while to adjust. This may cause your period to be delayed.