Hypothyroxinemia of prematurity and infant neurodevelopment: A pilot study

To assess whether hypothyroxinemia has specific effects on neurodevelopment in premature infants, thyroid hormone levels were determined at 2 weeks of life and 40 weeks postconceptional age (PCA), and infants were evaluated a t 3 months corrected age using the Bayley Scales of Infant Development and Early Infancy Temperament Questionnaire. Additional attention scales were d erived from the factor analysis of relevant Bayley items. Fifteen infants b orn between 30 and 35 weeks and 21 full-term infants were studied. Results indicated no group differences on the Bayley or derived attention scales, w hereas the temperament questionnaire revealed lower sensory thresholds and greater reactivity in the preterm group. The preterm group had normal thyro xine (T4) levels at 2 weeks of age, which declined by 40 weeks PCA for both free T4 (p < .01 for reference value and p < .0001 for gestational age-adj usted value) and total T4 (p < .05 for age-adjusted value). Correlations re vealed that higher 40-week PCA free T4 levels were associated with better a ttentiveness ratings (p < .01 for reference and p < .0001 for gestational-a ge values) and sustained attention (p < .05) and higher 40-week total T4 wi th better motor skills (p < .05 for gestational-age value). These findings signify that a mild degree of hypothyroxinemia is evident in preterm infant s without neurological risk and predicts subsequently poorer cognitive and motor abilities.