If the period is less than 2 days or more than 8 days, it is an abnormality and a medical examination is needed to determine the cause. In addition to the time of menstruation, we also need to determine whether the volume of menstruation is normal and whether the cycle of menstruation is normal. The volume of menstruation at menarche is normal between 20-60 ml, more than 80 ml is too much menstruation, less than 20 ml is too little menstruation, and the menstrual cycle is normal within 21-35 days. Due to the imperfect feedback mechanism of the gonadal axis at the time of menarche, there can be normal menstrual volume and menstrual period, but delayed menstrual cycle. As long as there is no organic lesion and no endocrine disorder, no treatment is needed and the menstrual cycle can return to normal three years after menarche.