Sudden bleeding with blood clots on the seventh day of menstruation may be caused by uterine fibroids, endometrial polyps or gynecological inflammation. 1. Uterine fibroids: most of the uterine fibroids are caused by heredity, hormone levels, gynecological inflammation stimulation, patients are often accompanied by menstrual abnormalities, which can be manifested as a sudden increase in menstrual flow on the seventh day of menstruation, accompanied by the phenomenon of blood clots. 2. Endometrial polyps: endometrial polyps are considered to be caused by high estrogen levels and long-term endometritis stimulation, mainly manifested as prolonged menstrual periods, non-menstrual bleeding, and if the polyp is larger, it is also prone to cause the phenomenon of blood clots. 3. Gynecological inflammation: If the patient suffers from endometritis, cervicitis or pelvic inflammatory disease, it may also affect menstruation, resulting in abnormal menstruation, prolonged menstruation, increased menstrual flow on the seventh day of menstruation, accompanied by the phenomenon of blood clots. It is recommended that patients with obvious menstrual abnormalities should seek prompt medical attention for symptomatic treatment.