Bright red menstrual blood during menstruation is considered to be caused by functional uterine bleeding, uterine fibroids, coagulation dysfunction and other factors. 1. Functional uterine bleeding: it belongs to the uterine bleeding caused by abnormal uterine structure, in which bleeding is the most important symptom of functional uterine bleeding, which is mainly manifested in the change of menstruation, due to the increase of bleeding, which leads to bright red menstrual blood. 2. Uterine fibroids: they are benign tumors formed by the proliferation of uterine smooth muscle tissues, and are one of the more common benign tumors in women. Many patients have no conscious symptoms, but when the size of fibroids increases, it can lead to abnormal menstruation, abdominal lumps, and abdominal cramps and other phenomena. Abnormal menstruation is mainly manifested in increased menstrual flow, long duration of menstruation, etc., and when bleeding increases, it can also lead to bright red menstrual blood. 3. Blood coagulation disorder: if the patient has blood coagulation disorder, it can lead to excessive menstrual blood during menstruation, so it can lead to bright red menstrual blood. In addition, endometrial cancer, thrombocytopenia, etc. can cause bright red menstrual blood. It is recommended to go to the hospital in time, under the guidance of the doctor to clarify the specific causes and give targeted treatment.