Having a large amount of blood clots fall out during menstruation is often clinically caused by the following reasons: 1. The most common submucosal fibroids or larger fibroids between the muscle walls can affect the contraction of the uterus when menstruation comes, so it can lead to a relatively large amount of menstruation, and the large amount of bleeding does not drain out of the uterine cavity in time, which can cause a large amount of clots caused by stagnant blood in the uterus, so it can manifest itself in menstruation as having a relatively large amount of 2. It may be caused by endometrial lesions that lead to large blood clots, for example, due to excessive endometrial hyperplasia or due to endometrial cancer, which may lead to large blood clots during menstruation. 3. It may be caused by functional uterine bleeding, such as estrogen deficiency or progesterone deficiency, which may lead to large blood clots during menstruation. The root of treatment is to find out the cause. It is recommended to go to the hospital for corresponding examination in time and give treatment according to the result.