What condition is characterized by bilious emesis occurring within hours after the first feeding?

The condition characterized by bilious emesis occurring within hours after the first feeding is duodenal atresia. This condition involves a congenital blockage of the duodenum, which is the first part of the small intestine. When the baby is fed, the milk cannot pass through the obstructed duodenum, leading to vomiting. The vomit can be bilious due to the presence of bile, as the obstruction typically occurs distal to the entry of bile into the gastrointestinal tract.

In contrast to other conditions that may cause vomiting in infants, the timing and nature of the emesis in duodenal atresia are distinctive. Pyloric stenosis typically presents with non-bilious projectile vomiting, occurring several weeks after feeding begins. Gastroesophageal reflux disease usually results in regurgitation rather than bilious vomiting and can occur at any time after feeding. Malrotation of the intestines may cause bilious vomiting, but it is generally accompanied by signs of intestinal obstruction and can take longer to present after feeding. Thus, the specific symptom of early bilious vomiting following the first feeding aligns most closely with duodenal atresia.