If menstruation occurs one month earlier than the other and the menstrual cycle keeps shortening, the most common causes are as follows: 1. Due to insufficient function of the corpus luteum and endocrine disorders, the corpus luteum appears to atrophy in advance, which is clinically manifested as a shortening of the menstrual cycle. This condition will also cause infertility, and should be actively given treatment. 2, due to uterine submucosal fibroids. As submucosal fibroids grow into the uterine cavity, the area of the endometrium increases, and the contraction of the uterus is affected by the protrusion of the fibroids into the uterine cavity. This will lead to shortening of menstrual cycle, prolongation of menstrual period and increase in menstrual flow. Therefore, it is recommended to have a sex hormone six test, and the blood should be drawn on the second or third day of menstruation. In addition, ultrasound examination is also needed, and it is recommended to draw blood for routine blood tests and coagulation time to rule out early menstruation caused by thrombocytopenia or coagulation disorders.