Sleeping hiccups in newborns are a common symptom, and causes of hiccups include poor diet, a cold abdomen, and gastroesophageal reflux disease (GERD). 1. Improper diet: when breastfeeding, if the milk is not enough or eat too fast, the newborn will inhale a lot of air, and the newborn will also inhale a lot of air when eating too much milk. Inhaled air will stimulate the diaphragm which will lead to hiccups when the newborn sleeps. 2. Cold abdomen: If the newborn’s abdomen is cold during sleep due to insufficient warming measures, the newborn’s diaphragm will be stimulated, resulting in diaphragmatic spasm, which will cause hiccups during sleep. 3. Gastroesophageal reflux disease (GERD): low pressure in the lower esophageal sphincter or low capacity of the tissues around the sphincter can cause GERD in newborns, which can lead to spitting up, restlessness and hiccups during sleep. There are many causes of hiccups in newborns. When a newborn is not feeling well, he or she should go to the hospital immediately for a clear diagnosis and targeted treatment.