Lack of a relation between human neonatal thyroxine and pediatric neurobehavioral disorders

The growth and differentiation of the central nervous system are closely related to the presence of iodine and thyroid hormones. It has been hypothesized that neurobehavioral disabilities of childhood, such as attention deficit hyperactivity disorder (ADHD), learning disorders, and autism can be attributed to fetal thyroidal endocrine disruption in utero. To determine whether there is an association between neonatal thyroid status and a subsequent diagnosis of a neurobehavioral disability, neonatal thyroxine (T₄) levels have been used as the indicator of the presence of intrauterine thyroidal dysfunction. Neonatal T₄ levels were obtained from the neonatal hypothyroidism screening program. All cases were diagnosed at medical school diagnostic clinics, the diagnostic categories being ADHD, autism spectrum disorder, behavioral disorder, cognitive disorder, developmental delay, emotional disorder, learning disability, and speech/language disorder. Conditional logistic regression analysis was performed for each clinical condition. Odds ratios for the conditions ranged from 0.92 to 1.13 with p values ranging between 0.19 and 0.84. No significant differences were detected between neonatal T₄ values of the cases and the controls for any of the neurobehavioral conditions. All neonatal T₄ values were within normal ranges. The data provide no evidence to suggest that intrauterine thyroid status as reflected by the neonatal T₄ values had an impact on the neurologic disorders diagnosed in childhood.