A sudden enlargement of the stomach may be caused by pregnancy, or it may be due to abdominal fluid accumulation, abdominal space-occupying lesions and so on. 1. Pregnancy: For women of gestational age, if you have recently noticed a sudden increase in the size of your stomach, along with symptoms such as menopause, you need to consider that it is due to pregnancy. 2. Peritoneal fluid: Peritoneal fluid, also known as ascites, is caused by any pathological condition that leads to an increase in the amount of fluid in the peritoneal cavity. There are many causes of peritoneal fluid, such as cardiovascular disease, hepatic disease, peritoneal disease, nutritional disorders, and so on. 3. Abdominal space-occupying lesions: if you suffer from abdominal space-occupying lesions, it will also cause your stomach to become bigger all of a sudden, and the common ones are intestinal tumors, pancreatic tumors, splenic tumors, and peritoneal and retroperitoneal tumors. There are many reasons why the stomach becomes bigger all of a sudden, so it is recommended to consult a doctor for examination and clear diagnosis. If it is caused by disease, it should be treated timely.