The menstrual cycle is a process that adult human women can go through. The menstrual cycle for a woman will repeat every 28 days while they are not pregnant. During this time, the women's ovaries create a mature ovum (egg). Then the woman's body prepares for pregnancy by thickening the walls of the uterus. If the woman does not become pregnant during this time, the egg and the lining of the uterus come out of the woman's body during menstruation.