OBJECTIVE: Thyroid hormones are essential for normal brain development. The aim of this study is to assess if high concentration of thyroid stimulating hormone (TSH) that is below the clinical threshold (5-15 mIU/L) at neonatal screening is linked to psychomotor development impairments in the offspring at preschool age.

DESIGN: A total of 284 Belgian preschool children 4-6 years old and their mothers were included in the study. The children were randomly selected from the total list of neonates screened in 2008, 2009 and 2010 by the Brussels newborn screening centre. The sampling was stratified by gender and TSH range (0.45-15 mIU/L). Infants with congenital hypothyroidism (>15 mIU/L), low birth weight and/or prematurity were excluded. Psychomotor development was assessed using the Charlop-Atwell scale of motor coordination. The iodine status of children was determined using median urinary iodine concentration. Socioeconomic, parental and child potential confounding factors were measured through a self-administered questionnaire.

RESULTS: TSH level was not significantly associated with total motor score (average change in z-score per unit increase in TSH is 0.02 (-0.03, 0.07), p=0.351), objective motor score (p=0.794) and subjective motor score (p=0.124). No significant associations were found using multivariate regression model to control confounding factors.

CONCLUSIONS: Mild thyroid dysfunction in the newborn-reflected by an elevation of TSH that is below the clinical threshold (5-15 mIU/L)-was not associated with impaired psychomotor development at preschool age.