This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Intestinal obstruction, Subject name: Surgery
A new born child has not passed meconium for 48 hours. What is the diagnostic procedure of choice? 
Select and explain. 
A. USG, B. Contrast enema, C. CT, D. MRI
B: Contrast enema
Answer: B: Contrast enema 
Explanation: Failure to pass meconium in the first 2 days of life (48 hours) is typically suggestive of a lower GI tract obstruction such as Hirschsprung's diseases, meconium plug syndrome or anorectal malformation. A contrast enema is the most suitable primary investigation to make the diagnosis, amongst the options provided.