The Relation between Neonatal Thyroxine Levels and Neurodevelopmental Outcome at Age 5 and 9 Years in a National Cohort of Very Preterm and/or Very Low Birth Weight Infants

Publisher Website
Google Scholar
Abstract
Transient neonatal hypothyroxinemia is very common in preterm infants. The literature on the effect of this hypothyroxinemia is, however, controversial, and large or long-term follow-up studies are not available. In a nationwide prospective follow-up study on very preterm and (or) very low birth weight infants (n = 717), we studied the relationship between thyroxine levels in the 1st wk of life and neurodevelopmental outcome at 5 y of age and school performance at 9 y of age. Thyroxine concentrations from filter paper eluates were determined in 717 infants: 32% had levels of more than 3 SD below the mean (<60 nmol/L). The percentage of infants with such low levels increased with decreasing gestational age. At the age of 5 y, 96% of survivors(n = 640) were available for extensive neurodevelopmental examination: 85 (13.3%) had a disability and 92 (14.3%) a handicap. At the age of 9 y, 83% of survivors (n = 552) answered a questionnaire on school performance: 300 (54.3%) were in mainstream education in a grade appropriate for age, 151 (27%) were in mainstream education with grade retention, and 101 (18.3%) were in special education. Both neurologic dysfunction at age 5 y and school failure at age 9 y were significantly related to lower neonatal thyroxine levels even after adjustment for other perinatal factors (odds ratio, 1.3). Whether this relationship is causal should be investigated. If a causal relationship exists, substitution therapy may at least partially prevent neurologic dysfunction and learning disabilities, both common sequelae of very preterm birth.