The menstrual cycle is the series of changes a woman's body goes through to prepare for a pregnancy. About once a month, the uterus grows a new lining (endometrium) to get ready for a fertilized egg. When there is no fertilized egg to start a pregnancy, the uterus sheds its lining. This is the monthly menstrual bleeding (also called menstrual period) that women have from their early teen years until menopause, around age 50.
However, it is not uncommon for some issues to occur. Talk to your doctor if you notice any big change in your cycle.