The pain in the stomach in the fourth month of pregnancy may be caused by the enlargement of the uterus, or it may be related to the miscarriage of the first sign or other reasons. 1. Enlargement of the uterus: the rapid development of the fetus in the fourth month of pregnancy, the uterus increases significantly, the enlarged uterus stretches the round ligament of the uterus, thus causing vague pain in the stomach. Generally easy to appear after exertion, after rest will be better, is a normal physiological phenomenon, do not have to worry. 2. Miscarriage with precursor: 4 months pregnant with a vague pain in the stomach may also be a sign of miscarriage with precursor, such as fatigue or sexual stimulation, external impact and other factors leading to miscarriage of pregnant women, there will be a vague pain in the abdomen, as well as lumbar pain, vaginal bleeding and other symptoms. General abdominal pain symptoms last a long time, can do ultrasound timely treatment of fetal preservation, bed rest, forbidden to have sex. 3. Other causes: 4 months pregnant stomach pain may also be cold, improper diet caused by gastroenteritis discomfort caused by abdominal pain, diarrhea and other symptoms. In addition, but also to check whether it is caused by pelvic inflammatory disease or adnexitis and other gynecological diseases, usually will appear leucorrhoea, odor and abdominal pain, discomfort, we must promptly check the cause of the vague pain in the stomach and treat the symptoms.