In girls, menstruation may occur clinically when the ovaries reach 4 by 3 by 1 centimeter. This is because the ovaries have matured and will periodically secrete estrogen and progesterone, which will result in the shedding of the uterine lining and the onset of menstruation. The majority of girls have their period between the ages of 13 and 15, and if they do not have their period after the age of 18, a detailed clinical examination must be done. The main purpose is to find out whether the uterus and ovaries are developing normally, and to find out whether the endocrine secretion is normal by analyzing the sex hormone six and thyroid function. If a girl has menstruation before the age of nine, the clinical diagnosis of precocious puberty can be made, accompanied by the development of breasts, and in this case, also go to the endocrinology department of the hospital as soon as possible for examination.