Impact of neonatal thyroid hormone insufficiency and medical morbidity on infant neurodevelopment and attention following preterm birth.

Background: Infants born preterm are at risk of both transiently reduced thyroid hormone levels and impaired neurocognitive development, including attention deficits. The objective of this study was to examine the effects of reduced thyroid hormone levels on general neurodevelopment and attention at 3 months corrected age.

Methods: Sixty-four infants born 24 to 35 weeks gestation were stratified into four gestational age groups: Group A, 23-26 weeks (n = 10); Group B, 27-29 weeks (n = 23); Group C, 30-32 weeks (n = 20); Group D, 33-35 weeks (n = 11). Controls were 33 healthy infants born full-term (Group E). In preterm only, free thyroxine (FT(4)), triiodothyronine (T(3)), and thyrotropin (TSH) were measured at 2 and 4 weeks of life and at 40 weeks postconceptional age. At 3 months corrected age, all infants were assessed with the Bayley Scales of Infant Development-Second Edition (BSID-II), from which both mental development index (MDI) and psychomotor development index (PDI) scores and four indices of attention were derived: sustained attention, selective attention, attention shift, and total attention.

Results: Gestational age-stratified preterm groups differed significantly in T(3) and FT(4) levels at 2 and 4 weeks of life in infants born less than 27 weeks gestation. Preterm infants overall scored significantly below full-term on BSID-II MDI and PDI, selective, sustained, and total attention scales. In the preterm group, FT(4) levels were positively associated with PDI and selective, sustained, and total attention.

Conclusions: Reduced levels of thyroid hormone in the neonatal period in preterm infants are associated with a reduced neurocognitive outcome in the attention domain at 3 months corrected age.