Bleeding before menstruation may be a normal physiological phenomenon, or it may be caused by luteal insufficiency, endometrial pathology and other reasons. 1. Normal physiological phenomenon: If there is a small amount of vaginal bleeding one or two days before menstruation, it may be normal menstrual bleeding, and it is considered that it may be caused by a small amount of endometrial shedding at the beginning of menstruation, which is a normal phenomenon, and there is no need to worry too much, and there is no need to intervene in a special way. 2. Luteal insufficiency: It is considered that it may be caused by prolonged overexertion, staying up too late, or excessive mental stress, etc. Luteal insufficiency may cause bleeding before menstruation, and may be accompanied by shortening of menstrual intervals, recurrent miscarriage and other symptoms. 3. Endometriosis: It is commonly seen in endometritis, endometrial cancer and other diseases, which can lead to small amount of vaginal bleeding before menstruation, and may be accompanied by abnormal leukorrhea, pelvic pain and other symptoms. If bleeding before menstruation is accompanied by other discomforts, it is recommended to consult a doctor as soon as possible for a clear diagnosis of the causative factors and treatment under the doctor’s guidance.