If you have a lot of blood clots during menstruation, it is often caused by the following reasons: 1) Inflammation of the endometrium, due to the endometrium inflammation leads to the endometrial tissue becomes brittle, so in the menstruation, the endometrium will be shed in large chunks, which will lead to clots in the menstrual blood in the clinic. 2) Submucous uterine fibroids, when there are uterine fibroids in submucous membranes, the fibroids will grow into the uterine cavity, which makes the uterine contraction decline. 3) The opening of blood sinus can also lead to clots in menstrual blood. 4) Submucous polyps can also lead to clots in menstrual blood. This makes the uterus contract less. 3, blood sinus opening can also lead to blood clots in menstrual blood. 4, uterine submucosal polyps can also lead to blood clots in menstrual blood. In addition, if the endometrial hyperplasia is too long, or due to other causes of endometrial lesions may also be the case of menstrual blood with blood clots. In this case, timely ultrasound examination should be done to exclude organic lesions, and diagnostic scraping can be done if necessary.