A neonate presents with bilious vomiting on day 2 of life. Abdominal X-ray shows the classic “double bubble” sign. What is the most likely diagnosis?

Correct option is B

“Double bubble” = gas in stomach + proximal duodenum with no distal gas → diagnostic of duodenal atresia, commonly associated with Down syndrome.
Explanation of options: (a) ✘ Pyloric stenosis = “single bubble” sign, non-bilious vomiting, seen later (2–6 weeks). (b) ✔ Correct; “double bubble” is pathognomonic for duodenal atresia. (c) ✘ Jejunal atresia → “triple bubble” sign, distal to duodenum. (d) ✘ Small bowel obstruction shows multiple air–fluid levels, not just double bubble.