Incidence of Congenital Hypothyroidism Over 37 Years in Ireland

In this study, we describe and analyze the significant increase in cases of CHT in the Republic of Ireland over a 37-year period. BACKGROUND AND OBJECTIVES:Congenital hypothyroidism (CHT) is one of the most common preventable causes of learning disability. Newborn screening with whole-blood thyroid-stimulating hormone measurements was introduced in the Republic of Ireland in 1979 and is coordinated from a single center with an unchanged protocol since its inception. Our objective in this study was to describe the incidence of CHT in the Republic of Ireland over the past 37 years in the context of a complete national population and an unchanged screening protocol.METHODS:The newborn screening records of all individuals who were diagnosed with CHT between 1979 and 2016 were reviewed. Infants with positive screening results had a whole-blood thyroid-stimulating hormone value of 15 mU/L at 72 to 120 hours of life; values of 8 to 15 mU/L required a repeat whole-blood screening test.RESULTS:Of 2361174 infants who were screened between July 1979 and December 2016, 1063 (662 girls) were diagnosed with CHT (incidence: 0.45 cases per 1000 live births). The number of detected cases increased from 0.27 cases per 1000 live births treated between 1979 and 1991 to 0.41 cases per 1000 live births treated between 1992 and 2004 to 0.65 cases per 1000 live births treated between 2005 and 2016. The increase in detected cases of CHT was predominantly in the normal or hyperplastic gland category.CONCLUSIONS:The incidence of CHT has increased significantly in the Republic of Ireland over the past 37 years despite a consistent screening cutoff. The increased rate was not explained by an increased survival rate of preterm infants or a changing population heterogeneity.