Neonatal Thyroxine, Maternal Thyroid Function, and Cognition in Mid-childhood in a US Cohort

Examine the associations of maternal thyroid hormones, maternal dietary information, and newborn T₄ levels with cognitive outcomes in mid-childhood.

We studied 921 children born 1999-2003 at gestational age ≥ 34 weeks, who were participants in Project Viva, a prospective pre-birth cohort study in Massachusetts. We examined maternal dietary information, maternal thyroid hormone levels, and neonatal levels of T₄. Research staff performed cognitive testing in mid-childhood (median age 7.7 years).

We included 514 women with measured first trimester thyroid hormone concentrations (mean 10.2 weeks); 15% of women had a thyroid stimulating hormone (TSH) level ≥ 2.5 mU/L, and 71% were college graduates. Newborn T₄ was collected from 375 infants (mean 17.6 μg/dl; SD 4.0), on day 2 (mean 1.9 days; SD 0.7) as part of the newborn screening program. Mean (SD) verbal and nonverbal IQ, memory, and motor scores of children were 113.2 (14.3), 107.1 (16.7), 17.1 (4.4), and 92.5 (16.6) points, respectively. In multivariable analysis, first trimester maternal thyroid function (total T₃, total T₄, free T₄, thyroid stimulating hormone (TSH) or total thyroid peroxidase (TPO) antibody levels) or newborn T₄ were not associated with any of the cognitive outcomes in mid-childhood after adjustment for sociodemographic and perinatal variables.

Maternal or neonatal thyroid hormone levels were not associated with cognitive outcomes in mid-childhood in this population with generally normal thyroid function. As we studied a highly educated cohort residing in an iodine-sufficient area, findings may not be generalizable.