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
Annular pancreas
Duodenal Atresia
Jejunal atresia
Oesophageal atresia