MODEL RELEASED. Acid reflux or vomiting. Full term pregnant woman holds a tissue to her mouth as she suffers from acid reflux or vomiting. Acid reflux is the regurgitation of stomach acid into the tube connecting the throat and stomach (oesophagus). It may cause a burning chest pain (heartburn) and can lead to oesophagus inflammation. Mild acid reflux is common in pregnancy. It is due to hormones causing inefficiency of the muscular valve at the lower end of the oesophagus. Hormone levels may also cause vomiting, particularly in the morning. Vomiting is usually, but not always, confined to early pregnancy. Severe and prolonged vomiting in pregnancy is called hyperemesis gravidarum.