An increase in stomach size can be caused by weight gain, pregnancy, excess gas and premenstrual syndrome, according to MedlinePlus. It is important for individuals to seek medical attention if symptoms of abdominal swelling are persistent, or if symptoms are accompanied by diarrhea, blood in the stools or fever.
Abdominal swelling can also be a symptom of ovarian cysts, blockages of the intestines or gallstones, according to Healthline. Individuals with cirrhosis of the liver are at risk for developing ascites, a condition that causes fluid to build up in the abdominal area. The condition does not usually cause symptoms in its early stages; however, excessive fluid build up over time can cause increased abdominal swelling and pain.