Changes in a woman's hormones that happen every month direct her body to release a tiny egg or ovum. The different stages in the production of this ovum are used to describe a woman's menstrual cycle. On average, the body produces an ovum once every 28 days and this is the average length of a menstrual cycle. Some women have longer or shorter cycles.
A woman's menstrual cycle begins with her period. To measure your own menstrual cycle, record the date of the first day you see blood during your period. The time from the first bleeding day of one period to the first bleeding day of the next period is the length of your menstrual cycle.
Women usually begin having periods in their early teens, but a woman's periods can start as early as age 9 or as late as 16 or 17. Having a period means that a woman's menstrual cycles have begun and that she can become pregnant if the ovum she releases combines with a man's sperm.