Abnormal bleeding means that it does not correspond to any of the normal menstrual cycle frequency, regularity, length of the period, or amount of menstrual bleeding. Therefore, to understand the difference between abnormal bleeding and menstruation, it is sufficient to know the cycle of normal menstruation and the volume of normal menstruation to distinguish them as follows: 1. Normal menstruation: It is cyclical as well as self-limiting, and the first day of bleeding is the beginning of the menstrual cycle. The interval between the first day of two menstrual periods is a menstrual cycle. The normal menstrual cycle is 21-35 days, the average is 28 days, and the duration of each period is 2-8 days, the average is 4-6 days. The normal menstrual volume is 20-60mL, more than 80mL is excessive menstruation, less than 5mL is called scanty menstruation. 2. Abnormal uterine bleeding: This is a common gynecological symptom and sign, including frequent menstruation with a cycle of less than 21 days, scanty menstruation with a cycle of more than 35 days, prolonged menstruation with a period of more than seven days, short menstruation with a period of less than three days, and also includes excessive menstruation and scanty menstruation.