Future research directions to identify causes of the increasing incidence rate of congenital hypothyroidism in the United States.

A workshop to evaluate the reported increasing trend in the incidence rate of primary congenital hypothyroidism (CH) identified by newborn screening was held February 27 and 28, 2008, in Atlanta, Georgia, and was sponsored by the Centers for Disease Control and Prevention, the Health Resources and Services Administration, and the National Newborn Screening and Genetics Resource Center. Through a series of presentations and discussions, this group of experts considered a variety of factors that could be contributing to the perceived increasing trend of the CH-incidence rate, the gaps in knowledge that need to be overcome to identify the causes of the observed trend, and possible future research activities that might resolve the uncertainties surrounding the increasing incidence rate of CH in the United States. On the basis of these discussions, workshop participants concluded that the initial focus of future efforts should be to determine if the increasing CH-incidence rate persists once there is standardization of the diagnostic criteria for the classification of CH versus transient hypothyroidism. In discussions, workshop participants suggested that if the increasing incidence rate of CH could not be explained by definitional issues, then future research could focus on the identification and evaluation of risk factors for CH that might be changing among the US population and, thus, contributing to the observed increasing incidence rate of CH.