This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
A new born child has not passed meconium for 48hrs. 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 suggestive of a lower GI tract obstruction such as Hirschprung disease, meconium plug syndrome or anorectal malformation. Ref: Paediatrics: Just The Fact's By Green, Franklin, 2004, Pages 114-15; Practical Paediatrics By Robinson, Robeon, 2003, Page 228