The changing epidemiology of congenital hypothyroidism: fact or artifact?

Screening increases prevalence estimates for most diseases and congenital hypothyroidism (CH) is no exception, affecting one in 6700 children by clinical ascertainment and one in 3500 in the first surveys of systematic biochemical screening of newborns. Importantly, screening has resulted in the disappearance of intellectual disability due to CH. A further doubling in prevalence estimates has recently been reported, mostly accounted for by changes in screening algorithms; accordingly, the prevalence of overt CH has remained stable. Population-based registries that distinguish confirmed diagnoses from positive screening results have proved invaluable. These registries should include: etiology of CH based on imaging, ideally technetium scintigraphy; ethnicity; socio-educational data; input from the screening laboratories and pediatric endocrinologists. Efforts should now be directed at increasing the proportion of the world's newborns screened for overt CH (currently 30%) and at determining if neonates with mild hyperthyrotropinemia also benefit from early treatment.