Normally, a woman’s menstruation is non-clotting, so there are no blood clots. If menstrual blood appears in clots, it is often due to the following reasons. 1. submucosal fibroids, or large fibroids between the muscle walls, which affect the contraction of the uterus to open the blood sinuses, causing an increase in menstrual flow and a large number of blood clots. 2. inflammation of the endometrium that causes the endometrium to shed large clots during menstruation, forming menstrual blood with blood clots. 3. corresponding endometrial The endometrium has corresponding lesions, such as endometrial cancer, atypical endometrial hyperplasia, simple hyperplasia of the endometrium or functional uterine bleeding, which can lead to blood clots in menstruation.