Reasons for frequent fetal hiccups in late pregnancy From a physical point of view, the reason for frequent fetal hiccups in late pregnancy may be caused by residues in the stomach. When pregnant women eat, food and liquids are passed into the stomach, and these foods and liquids may be aspirated by the fetus into the airway and cause hiccups. In addition, hormonal levels in pregnant women can also have an impact on the fetus in the third trimester. These hormones may cause excess gas in the stomach and cause hiccups. In addition, frequent hiccups in the fetus may also be due to the development of the brain and central nervous system.