Heavy blood clots during menstruation may be caused by physiological factors, gynecological diseases, blood system diseases and other factors. 1. Physiological factors: some women may bleed more during menstruation, and when the blood is not discharged in time in the uterine cavity, it usually forms a blood clot. 2. Gynecological diseases: If you suffer from endometrial polyps, endometrial thickening, submucosal fibroids and other diseases, it may affect the changes in the amount of bleeding. In addition, when menstruation comes, the endometrium in the diseased area irregularly sheds large pieces and mixes with the menstrual blood, which may cause a lot of blood clots in menstruation. 3. Blood system diseases: Suffering from thrombocytopenia, leukemia, anemia and other diseases, coagulation dysfunction may cause increased menstrual flow and clot-like manifestations. Clinical symptoms of blood clots in menstruation is recommended to go to the hospital, under the guidance of the doctor according to the cause of the disease, targeted treatment.