It is normal to have menstrual periods without clots or with a small amount of very small clots. Because menstrual blood itself is not clotted, if there are relatively large clots in menstrual blood, which are often accompanied by dysmenorrhea in clinical practice, it is often due to the following reasons: 1. submucosal fibroids, because submucosal fibroids are growing into the uterine cavity, so they cause a relative increase in the endometrial area, which also affects the contraction of the uterus. So make the blood sinus open relatively longer, so that the phenomenon of menstrual blood with blood clots is formed; 2, caused by inflammation of the endometrium, when the endometrium has inflammation, the endometrial tissue will be shed in large pieces when coming to menstruation, so it will cause the phenomenon of blood clots; 3, in the clinical have endometrial lesions, or functional uterine bleeding, may lead to the phenomenon of blood clots, so For this condition, a detailed gynecological examination should be done and then treatment should be given.