Menstruation-your period-is just one part of a larger menstrual cycle. As women grow older and become reproductively mature, we all develop a menstrual cycle. During this cycle, your uterus will prepare to house a fertilized egg. If the egg is not fertilized and you are not pregnant, then the lining is not needed and is shed. It is this shedding of the uterine lining that is called your period. This cycle repeats itself month after month until you reach menopause.

The process is an intricate one, controlled by the brain and a complex, hormone-signaling system. Although menstrual cycles can vary in length, the number of days between ovulation and your menstrual period is consistent-approximately 14 days (11-16 is the normal variation). For example, if your typical cycle length is 31 days, then the first half of the cycle is 16 days and ovulation occurs on the 17th day.

But the menstrual period is only one part of the cycle that takes place each month until you are in your 40s or 50s.