Women’s menstrual period refers to the period of menstrual bleeding, calculated from the first day of menstrual bleeding, and the end time is calculated according to the complete disappearance of menstruation. As long as a woman’s menstrual bleeding time is maintained within 3-7 days, it is a normal menstrual bleeding time and does not require special adjustment. If the menstrual bleeding time is less than 3 days, it may be caused by the abnormal thickness of the endometrium and needs to be regulated by ultrasound examination. The calculation of menstrual periods is not particularly strict and does not need to be strictly defined by the 24 hours of the day, as long as vaginal bleeding occurs, it is a sign of the beginning of menstruation.