Bilious vomiting in the newborn includes the full differential (duodenal atresia, midgut malrotation and volvulus, jejunoileal atresia, meconium ileus and necrotizing enterocolitis), but rapidly-ill bilious vomiting combined with fever, distension, and tenderness after a few days to a week or so is most concerning for midgut volvulus. Most other causes present soon after birth with the exception of necrotizing enterocolitis, usually affecting premature babies within a couple of weeks after birth. Diagnosis with upper GI.