Transient hypothyroxinemia of prematurity and problem behavior in young adulthood

Introduction Preterm newborns are at risk of developing transient hypothyroxinemia of prematurity (THoP), which has been associated with subsequent neurodevelopmental impairments. Behavioral outcomes at adult age after THoP have never been reported. Aim To examine whether there is an association between THoP and problem behavior at young adult age. Methods This study was part of the follow-up of 19-year-old subjects born very preterm (i.e., <32 weeks) and/or with a very low birth weight (i.e., <1500 g) from the Project On Preterm and Small-for-gestational-age infants (POPS) cohort. We included 468 subjects of the POPS cohort; of whom 123 had THoP. Thyroxine (T4) concentrations were obtained through the national neonatal screening program for congenital hypothyroidism. THoP was defined as a T4 concentration <-3 SD (approximately 60 nmol/L). At age 19, behavior was assessed using the Young Adult Self Report and the Young Adult Behavioral Checklist for parents. Results THoP was associated with a 1.8 (95% confidence interval (CI): 1.01–3.4) −fold increased odds of self-reported Internalizing behavior, as well as with a 1.9 (95% CI: 1.1–3.1) −fold increased odds of parent-reported Total problem behavior. These relations persisted after correction for demographic and perinatal variables. Similar associations were absent for the other self-reported and parent-reported syndrome and problem scales. Conclusions THoP was associated with more internalizing and total problem behavior at age 19. While our observations warrant more awareness of problem behavior in preterm infants, at present, it is unclear whether these associations are causal and screening for THoP does not seem necessary.