The best indicator for monitoring the impact of the Iodine Deficiency Disorders Control programme is -

<p> Iodine deficiency disorder control: 1. Iodized salt:- Most widely used prophylactic measure against endemic goitre. In India the level of iodization is fixed under the Prevention of Food Adulteration Act(PFA) and is not less than 30 ppm at the production point, and not less than 15 ppm of iodine at the consumer level. Iodized salt is most economical , convenient and effective means of mass prophylaxis in endemic areas. Under the national IDD control activities , government of India proposed to completely replace common salt with iodized salt in a phased manner. 2. Iodized oil 3. Man power training 4. Mass communication 5. Iodine monitoring: countries implementing control programmes require a network of laboratories for iodine monitoring and surveillance. These laboratories are essential for iodine excretion determination, determination of iodine in water, soil and food and determination of iodine in salt for quality control. Neonatal hypothyroidism is a sensitive pointer to environmental iodine deficiency and can thus be as effective indicator for monitoring the impact of a programme. {Reference: Park&;s textbook of community medicine 23 rd edition, pg no. 644}