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: Social & Preventive Medicine
The most sensitive indicator of environmental iodine deficiency is 
Select and explain. 
A. Serum T4 levels, B. Serum T3 levels, C. Urine iodine excretion, D. Neonatal hypothyroidism
D: Neonatal hypothyroidism
Answer: D: Neonatal hypothyroidism 
Explanation: Ans. d. Neonatal hypothyroidism