Butt pain in the 8th month of pregnancy may be caused by the following reasons: First, the 8th month of pregnancy belongs to the late stage of pregnancy, the uterus enlarges very obviously, the pregnant woman’s abdominal protrusion makes the abdomen lean forward and drop for a long time, which increases the burden on the caudal vertebrae and causes butt pain. Second, in late pregnancy, as the number of weeks of pregnancy increases, the hormones in the body change in order to adapt to the approaching labor, and the relaxin increases, making the ligaments of pregnant women gradually relax, and the body will lean backward, the center of gravity shifts backward, increasing the pelvic compression and making the buttocks pain. Third, the increase of relaxin makes the sacral ligaments relax, resulting in the lack of stability of the pelvis, which will also pull the muscles and nerves of the pelvis when moving, causing buttock pain. The pressure of the uterus on the pelvic nerves, the pressure of the enlarged uterus on the abdominal aorta and the inferior vena cava, causing pressure on the inferior vena cava and the nerve plexus, resulting in buttock pain due to nerve ischemia.