The menstrual period is the duration of menstruation in girls, and the cycle refers to the time between the first day of two menstrual periods. The menstrual cycle and menstrual period of most girls are relatively constant, and a very small number of them may experience an early or delayed menstrual period. Normal menstruation is cyclical and self-limiting. The duration of each menstrual period is called the menstrual period, which is the period between the first day of vaginal bleeding and the cessation of vaginal bleeding, which is 2-8 days for normal girls and 4-6 days on average. The menstrual cycle is the time flat between the first day of two menstrual periods, usually 21-35 days, an average of 28 days. In clinical practice, prolonged menstrual period exceeding 8 days, or accompanied by excessive menstrual bleeding, each time bleeding more than 80 ml is an abnormal phenomenon, need to consult a doctor in time.