If a newborn has vomiting of yellow water mucus, it is mainly considered to be caused by the following reasons: First, it is caused by the newborn inhaling a large amount of amniotic fluid. The newborn swallows a lot of amniotic fluid while in the mother’s womb. After the newborn is born, he or she will vomit yellow water. This is a normal physiological phenomenon as the newborn naturally expels the amniotic fluid. If the symptoms of vomiting are not particularly serious, parents do not need special treatment. Secondly, it is caused by congenital pyloric obstruction and other diseases of the digestive tract. If the newborn has congenital pyloric obstruction, in this case, the newborn’s stomach is very high tension, there will be serious vomiting, and even bile will be vomited. Because the bile of the newborn is yellow, in this case the newborn will vomit milk along with the bile, thus manifesting itself as yellow watery mucus.