The following are the causes of menstrual blood flow: 1. The cervical surgery, abortion surgery, and uterine cleansing surgery have caused local adhesions in the cervix and narrowed the cervical canal, so the menstrual blood flow will not be smooth. 2. 3. Due to local lesions of the cervix, such as cervical fibroids and cervical polyps, which can narrow the cervical canal and cause menstrual blood to flow out smoothly.