A vague pain in the abdomen in the fifth month of pregnancy may be caused by physiological reasons, premature miscarriage and acute gastroenteritis. 1. Physiological reasons: after pregnancy, the enlarged uterus will pull the ligaments of the uterine floor and press the pelvic floor tissues, which will cause vague pain in the abdomen, which is a physiological phenomenon that does not require special treatment, and can be relieved after proper rest. 2. Pre-eclampsia: It can also cause vague pain in the abdomen, accompanied by a small amount of vaginal bleeding, combined with medical history, clinical manifestations and ultrasound examination can assist in the diagnosis. 3. Acute gastroenteritis: can also cause vague pain in the abdomen, accompanied by diarrhea, fever, etc., most of the unclean diet or improper diet history, combined with medical history and clinical manifestations can help diagnosis. In the clinical five months pregnant with a vague pain in the abdomen need to go to the hospital, in order to identify the cause, and actively deal with.