For women of childbearing age, menstruation is accompanied by an autonomous thickening of the uterine lining, a functional cyclical change that prepares the uterus for embryo implantation. Normal women of childbearing age will ovulate once a month, and after ovulation, due to the hormone levels acting on the endometrium, an autonomous thickening will occur, so as to provide a suitable “hotbed” for embryo implantation. If there is no conception in that month, the endometrium will peel off again with the hormonal changes and be discharged with bleeding. This cyclical vaginal bleeding is called menstruation. Therefore, if a woman does not have her period after a delay of more than ten days, she may consider whether she is pregnant. In addition, monthly menstruation causes a woman to lose some of her blood, giving the hematopoietic function a workout and also preventing excess iron in the body.