Bleeding in the third trimester of pregnancy can be caused by pre-miscarriage, cervical polyps, or cessation of embryonic development. 1. Pre-eclampsia: Pre-eclampsia is caused by the separation of the embryonic tissue from the uterine lining. Early preeclampsia is initially characterized by only a small amount of bleeding, which varies, is irregular or continuous, or is accompanied by the discharge of blood clots, and is accompanied by symptoms such as abdominal pain and lumbago. 2. Cervical polyps: During pregnancy, estrogen in a woman’s body will rise, which will cause cervical polyps, thus causing vaginal spotting and bleeding. 3. Cessation of embryonic development: If the fetus itself has chromosomal abnormalities, or the development of vital organs is not normal, it will cause bleeding. If the patient has symptoms of bleeding in the third trimester of pregnancy, she should go to the hospital in time to find out the cause and get treatment under the guidance of professional doctors.