Low volume and dark color on the first day of menstruation is a normal condition. Menstruation is the periodic shedding and bleeding of the endometrium that accompanies the cyclical changes of the ovaries. The menstrual blood itself is dark red in color. In addition to blood, there is a small amount of endometrial debris, cervical mucus and shed vaginal epithelial cells. The amount of menstrual blood is usually small on the first day, then gradually increases each day and decreases again by 4-5 days. Menstrual blood is usually non-clotting, but clots can occur when bleeding is heavy or rapid. The normal menstrual cycle is 21-35 days, with an average of 28 days. A period is 2-8 days, with an average of 4-6 days. The volume of menstruation is the total amount of blood lost during a period, which is normally 20-60 ml, and more than 80 ml is considered excessive menstruation.