No association between transient hypothyroxinaemia of prematurity and neurodevelopmental outcome in young adulthood

Context: Transient hypothyroxinaemia of prematurity (THoP) has been associated with neurodevelopmental impairment in infancy and childhood. It is not known whether these relations persist into adulthood. Objective: To examine whether there is an effect of THoP on intelligence quotient (IQ) score and motor functioning at young adult age. Design: This study was part of the 19-year follow-up of the Project On Preterm and Small-for-gestational-age birth (POPS) cohort, which included infants born very preterm (i.e., <32 weeks) and/or with a very low birth weight (i.e., <1,500 g). Setting: Multicenter study Patients: 398 19-year-old participants of the POPS cohort, of whom 120 had THoP. Exposure: Thyroxine (T4) concentrations were obtained through the national neonatal screening program for congenital hypothyroidism. THoP was defined as a total T4 concentration <-3 SD of the daily mean (approximately 60 nmol/L). Main outcome measures: IQ and motor functioning, measured with the digital Multicultural Capacities Test-Intermediate Level and a revised version of Touwen’s examination of minor neurologic dysfunction, respectively. Results: THoP was not associated with IQ score (mean difference: 0 (95% confidence interval: -3.8 to 3.8) points) or motor function (mean difference: 0.6 (95% confidence interval: -1.3 to 2.5) points) after adjustment for demographic and perinatal characteristics. Conclusions: No associations between THoP and neurodevelopmental outcome at age 19 years were found.