How does schoolgirl have a month to do not have menstruation to return a responsibility

Menstruation is the female endometrium in estrogen, progesterone under the joint action, periodic shedding and bleeding phenomenon called menstruation. Menstruation cycle is generally 28-30 days, menstrual period is 3-7 days. Girls do not come to menstruation a month, because the hypothalamus-pituitary-ovarian gonad axis has just been established, but it is not mature, generally takes 3-5 years to mature. Immature signs for the menstrual period, estrogen luteinizing hormone positive feedback is difficult to establish, can not ovulation, no ovulation on the production of progesterone, endometrium for a long time in a single estrogen, resulting in irregular vaginal bleeding and irregular menstruation, this is a normal physiological phenomenon, do not do too much intervention treatment.