Most pregnant women have symptoms of gastroesophageal reflux disease (GERD), especially heartburn, at some point. These symptoms may start at any time during a pregnancy, and often get worse throughout the pregnancy. Heartburn is common when you are pregnant. That's because hormones cause the digestive system to slow down. The muscles that push food down the esophagus also move more slowly when you are pregnant. And as the uterus grows, it pushes on the stomach. This can sometimes force stomach acid up into the esophagus.