Sudden discharge of large amount of blood clots during menstruation is considered to be caused by irregular menstruation, endometrial thickening, submucosal fibroids, which need to be treated with medication or surgery according to the specific causes. 1. Irregular menstruation: mainly due to endocrine disorders, which can cause significant increase in menstrual flow and sudden discharge of a large number of blood clots. You need to take medication under the guidance of a doctor to regulate menstruation, such as progesterone capsules. 2. Endometrial thickening: If the thickness of the endometrium is more than 14mm, it can lead to prolonged menstrual period, increased menstrual flow and sudden discharge of large amount of blood clots, which can be treated by scraping. 3. Submucosal fibroids: due to the continuous growth of fibroids will invade the uterine lining, which will also cause the discharge of a large number of blood clots, and need to be surgically removed. If the above symptoms occur, patients should go to the hospital in time to avoid delaying the condition.