A newborn develops progressive conjugated hyperbilirubinemia with pale stools. What is the most likely diagnosis?

The presence of progressive conjugated hyperbilirubinemia in a newborn, along with pale stools, strongly indicates an issue related to biliary flow. Biliary atresia is a congenital condition where the bile ducts are absent or malformed, leading to impaired bile drainage from the liver to the intestine. This obstruction causes an accumulation of conjugated bilirubin in the bloodstream, resulting in jaundice.

Additionally, the pale stools are indicative of a lack of bile reaching the intestine. In healthy infants, bile pigments contribute to the coloration of stools; therefore, pale stools often suggest that there is not enough bile being secreted, aligning with the diagnosis of biliary atresia.

While conditions like hepatitis could also cause jaundice in a newborn, they typically do not present with pale stools due to obstruction of bile flow. Neonatal sepsis might show elevated bilirubin levels secondary to infection, but it does not explain the specific finding of pale stools. Hemolytic disease of the newborn often presents with unconjugated hyperbilirubinemia rather than conjugated and does not typically result in pale stools either. Thus, the combination of conjugated hyperbilirubinemia and pale stools points most specifically to biliary atresia.