Spitting up after a baby falls asleep may be due to gastroesophageal reflux, improper feeding, digestive system diseases and other factors. 1. Gastroesophageal reflux: the baby after birth, especially in the first three months of the stomach is in a horizontal position, and the lower esophageal dilatation muscle and the fundus of the stomach is not mature, the pylorus of the tension is relatively high, so it is easy to cause the baby fell asleep spit up milk. 2. Improper feeding: If the baby ate too much before going to bed, more than the stomach capacity, after falling asleep, the milk is easy to reflux from the stomach to the mouth, causing spitting up. In addition, if the baby sucks milk, swallow more air, will also be prone to spit up. 3. Digestive system diseases: due to the baby’s abdomen is cold or intestinal infection bacteria, germs, can lead to the baby fell asleep after spitting up, but also accompanied by diarrhea, abdominal pain and other manifestations. In addition to intussusception, pyloric hypertrophy obstruction, intestinal obstruction and other diseases can lead to the baby fell asleep and spit up. The baby fell asleep after spitting up, there may be other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.