The duration of menstrual bleeding is usually 2-8 days, with an average of 4-6 days. The amount of menstrual flow is the total amount of blood loss in one menstrual period, normal menstruation is 20-60 ml, the amount of menstrual flow is more than 80 ml, usually the amount of menstrual flow of blood on the first 1-2 days of the most, and the rest of the days are usually a small amount of bleeding or brown, coffee-colored vaginal discharge. Normal menstrual blood is dark red, because in addition to blood, there are also shed endometrial debris, inflammatory cells, cervical mucus and shed vaginal epithelial cells. Because menstrual blood contains some proteases, it is non-coagulative. Clots in menstrual blood or darkening of the color of menstrual blood can also be formed if the bleeding rate is too fast flow and excessive bleeding.