Stomach pain in the fourth month of pregnancy may be caused by physiological factors, pre-miscarriage, gastrointestinal diseases and other factors. 1. Physiological factors: the uterus gradually increases in size during the fourth month of pregnancy, which may cause the round ligaments of the uterus to be stretched, and you will feel mild pain in the lower abdomen, which may gradually improve after bed rest. 2. Pre-eclampsia: Strenuous exercise or over-exertion may induce pre-eclampsia, which will cause stomach pain and may be accompanied by vaginal bleeding. 3. Gastrointestinal diseases: after pregnancy, due to the weakening of gastrointestinal digestion and absorption ability, improper diet, may induce gastrointestinal lesions, such as indigestion, acute gastroenteritis, etc., which will induce stomach pain, may also be accompanied by abdominal pain, vomiting, diarrhea and other symptoms. Pregnant women four months stomach pain may also be other causes, and there are other abnormal manifestations, pregnant women should promptly seek medical examination and treatment, to avoid causing serious consequences.