Under normal circumstances, there will be no blood clots when you have your period because menstrual blood does not clot. If there is blood clot in menstrual blood, it is often caused by the following reasons: 1. submucosal fibroids, due to the growth of fibroids into the uterine cavity, the relative increase of the endometrial area, poor contraction of the uterus, and the opening of blood sinuses, it will lead to blood clots in menstrual blood. 2. inflammation of the endometrium, endometrial polyps, or the appearance of endometrial The presence of endometrial lesions, such as cancer of the endometrium, may lead to blood clots in menstrual blood. Therefore, if there is blood clot in menstrual blood, it is recommended to do detailed examination, such as blood routine, clotting time, ultrasound, gynecological examination, and give appropriate treatment according to the results.