Aetiology of congenital hypothyroidism in Finland

In Finland a nationwide screening programme for congenital hypothyroidism (CHT) has operated since 1980 with complete coverage. Among the total of 307,000 newborns screened, the incidence per 100,000 was 24.6 for thyroid dysgenesis and 4.0 for dyshormonogenesis. We conclude that, when screening is based on cord serum TSH, the false-positive results are caused mainly by difficult delivery. The most important factors associated with dyshormonogenesis were CHT in the family, origin from a geographic risk area, and origin of both mother and father from the same community. These reflect the autosomal recessive inheritance. The risk factors for dysgenesis were female gender, CHT in the family, birth in a geographic risk area, and birth during a risk period of the year.