It is not normal for a woman to have her period for 20 days. Usually women have a menstrual cycle of 21-35 days, with an average of about 28 days, which can be 1 week early or 1 week late. Normal menstruation is cyclical and self-limiting. If the menstrual cycle is shorter than 21 days, it belongs to frequent menstruation, mostly due to disease factors, such as luteal insufficiency, organic lesions of the reproductive system, anovulatory dysfunctional uterine bleeding: 1. Luteal insufficiency: causing early atrophy of the corpus luteum, it will come early, you can have a sex hormone six test and take progesterone orally in the second half of the menstrual period for 2, reproductive system organic lesions: for example, some women suffer from submucosal fibroids, endometrial polyps or endometrial malignant lesions, which can lead to early menstruation. Ultrasound examination can be performed in time to clarify whether there is abnormal thickening of the endometrium or whether the echogenicity is uniform, diagnostic scraping can be performed, and then corresponding conditioning can be given according to the pathological diagnosis; 3, anovulatory abnormal uterine bleeding: such causes can lead to frequent menstruation, completely irregular menstruation, often not accompanied by dysmenorrhea, and may cause blood loss anemia.