Drugs.com indicates that simethicone, the active ingredient in over-the-counter gas medications like Gas X, has not been categorized by the Food and Drug Administration due to insufficient controlled data. Medical authorities on safe drugs during pregnancy have indicated that simethicone is likely not harmful during pregnancy.
According to the American Pregnancy Association, increased gas during pregnancy is mainly attributable to an increase in progesterone levels. The progesterone causes the digestive system to slow which allows for more gas to build up during digestion. Added pressure from an enlarged uterus in late pregnancy may also cause increased gas. The American Pregnancy Association recommends thoroughly chewing food, avoiding fried foods, drinking water and exercise to help control gas build up.