In case of new born the commonest cause of intestinal obstruction is -

Congenital atresia and stenosis are the commonest cause. The incidence of atresia varies with anatomical site: duodenum - 35percent jejunum - 15percent ileum - 25percent  ascending colon - 10percent multiple sites  - 15percent Vomiting is bile stained or not, depends on the atresia proximal or distal to ampulla of vater. In 85% of cases the atresia is distal to the ampulla, therefore the vomiting is bilious. Approximately 1/3 of newborns with duodenal atresia have associated Down's syndrome. The 'double bubble seen on the air contrast upper GI series is characteristic of duodenal atresia. Treatment of choice is - Duodenoduodenostomy