**2. Epidemiology**

The incidence of CH varies from 1 in 4000 to 1 in 1000 in newborn infants as has been reported from various parts of world [5]. Developing countries like India and Iran have a higher incidence of CH [6, 7]. In countries like The US, Canada, New Zealand, Italy, Greece and Argentina the incidence of CH has nearly doubled since the introduction of newborn screening programmes [5, 8–12]. Widespread lowering of screening cutoffs in newborn screening programs [5, 8], increase detection of milder cases of CH, increase screening of higher risk newborn preterm and low birth infants, increased number of birth among Hispanic and of low birth weight [13] are some of the supposed causes that have been proposed as a possible cause for the increase in the incidence of CH. The incidence of CH is higher among Hispanic and Asian individuals and lower in black individuals [10, 13]. There has been a dramatic increase in the incidence of congenital hypothyroidism detected by the newborn screening programs, the incidence has risen from 1:3985 (in 1987) to 1:2273 (in 2002) [14]. This dramatic increase may be attributed to a spurt in the Asian (37%) and Hispanic (53%) births over the same period [13].
