Congenital Hypothyroidism and School Achievement in Adolescence: A Population-based Sibling Control Study

Abstract

To study school achievement in grade 9 of compulsory school in children with congenital hypothyroidism (CH), both those detected by the national screening program and those with a normal screening result and thus diagnosed later. Nationwide study of children in the Swedish Medical Birth Register (n=1,547,927) from 1982 through 1997, linked to the neonatal screening CH cohort and the National School Register. Dried blood spot (DBS) samples are collected from all newborn infants, according to the neonatal screening program. Thyroid stimulating hormone (TSH) was used for CH screening. CH was defined as either having an abnormal screening result (DBS+) and treatment with levothyroxine, (LT4+), or having a normal screening result, but a CH diagnosis in the National Patient Register and treatment with LT4 (DBS-/ICD+/LT4+). Regression models were used to study school performance measured as grade point sum and national test results. Sibling analysis was also performed to account for unmeasured familial factors. There were 448 DBS+/LT4+ and 475 DBS-/ICD+/LT4+ children. Children with CH had lower grade point sum, adjusted β=- 6.34 (95%CI: -11.7,-1.01) and adjusted β= -10.3 (95% CI:-15.5,-5.20) for those with abnormal (DBS+/LT4+) and normal screening (DBS-/ICD+/LT4+) results, respectively. CH was also associated with lower result on the national tests, especially in mathematics. These associations remained in the sibling analyses. Youth with CH had slightly lower school achievements compared with those without CH and compared with their siblings. CH children with a normal screening result, and thus diagnosed later, presented the lowest results on grade point sum and national tests.