Menstruation usually occurs once every 21-35 days, with an average of 28 days. If it is within this range, it is normal. The duration of each period is called the menstrual period, which is usually 2-8 days, with an average of 4-6 days. The volume of menstruation is the total amount of blood lost during one period. The normal volume of menstruation is 20-60mL, and more than 80mL is called excessive menstruation. Menstruation is an important physiological phenomenon for women during the physiological period. Menstruation is the periodic shedding and bleeding of the endometrium that accompanies the cyclical changes of the ovaries, and the appearance of regular menstruation is an important sign of the maturity of reproductive function. Usually, menstrual blood is dark red in color and contains, in addition to blood, endometrial debris, cervical mucus, and shed vaginal epithelial cells. If abnormal menstruation occurs, such as low menstrual flow or prolonged absence of menstruation, the patient must go to the hospital for prompt examination.