Relatively little is known in euthyroid populations about the changes in maternal thyroid hormones during pregnancy, the nature of the relationship to cord thyroid hormone levels, and subsequent infant neurodevelopment. The aim of the study was to describe the relationship between maternal and cord thyroid hormone parameters and to describe their associations with neurodevelopment at 5.5 years. We conducted a follow-up of women and their children born at or over 37 weeks' gestation. We measured maternal levels of TSH, thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), T(4), and free T(4) (FT(4)) at 10 and 34 weeks and at delivery, and cord levels of T(4), FT(4), TPOAb, and TgAb. The association of cord thyroid hormone parameters with McCarthy scale scores adjusted for the major confounders of neurodevelopment. Fifteen percent of the women were TPOAb-positive, and 12% were TgAb-positive; the proportion of women with mildly elevated TSH levels increased during pregnancy with the maximum (14%) at delivery. Lower perceptual performance and motor scores were found with TgAb-positive women and lower perceptual performance scores with TgAb-positive cord levels; otherwise, unadjusted maternal levels of TPOAb, TgAb, and TSH and unadjusted cord levels of FT(4), TPOAb, and TgAb were not associated with neurodevelopment at 5.5 years. Low cord T(4) levels were associated with significant increments in four McCarthy scales: General Cognitive Index, Verbal, Quantitative, and Memory scales-increments that persisted after adjustment at 11.4, 7.8, 7.6, and 7.8 points, respectively. Lower levels of cord T(4) were associated with increments in the McCarthy scales in the domains that tested cognitive and verbal abilities at 5.5 years.
