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Neonatal Thyroxine, Maternal Thyroid Function, and Child Cognition

Department of Ambulatory Care and Prevention (E.O.), Harvard Medical School and Harvard Pilgrim Health Care, Boston, Massachusetts 02215; Section of Endocrinology, Diabetes, and Nutrition (L.E.B., S.L.L., E.N.P.), Boston University Medical Center, Boston, Massachusetts 02118; Department of Obstetrics and Gynecology (D.P.), Harvard Vanguard Medical Associates, Boston, Massachusetts 02215-3904; and New England Newborn Screening Program (M.L.M.), University of Massachusetts Medical School, Boston, Massachusetts 01655

Address all correspondence and requests for reprints to: Emily Oken, M.D., M.P.H., 133 Brookline Avenue, Boston, Massachusetts 02215. E-mail: emily_oken{at}hphc.org.

Context: Thyroid hormone is essential for normal brain development. Limited data are available regarding whether thyroid function in neonates influences later cognitive development.

Objective: Our objective was to study associations of newborn T₄ levels with maternal thyroid function and childhood cognition.

Design and Setting: We studied participants in Project Viva, a cohort study in Massachusetts.

Participants: We studied a total of 500 children born 1999–2003 at 34 wk or more.

Main Outcome Measures: We determined cognitive test scores at ages 6 months and 3 yr.

Results: Mean newborn T₄ at a mean age of 1.94 d was 17.6 (SD 4.0) µg/dl, and levels were higher in girls [1.07 µg/dl; 95% confidence interval (CI) 0.38, 1.76] and infants born after longer gestation (0.42 µg/dl; 95% CI 0.17, 0.67 per wk). Newborn T₄ levels were not associated with maternal T₄, TSH, or thyroid peroxidase antibody levels. On multivariable linear regression analysis, adjusting for maternal and child characteristics, higher newborn T₄ was unexpectedly associated with poorer scores on the visual recognition memory test among infants at age 6 months (–0.5; 95% CI –0.9, –0.2), but not with scores at age 3 yr on either the Peabody Picture Vocabulary Test (0.2; 95% CI –0.1, 0.5) or the Wide Range Assessment of Visual Motor Abilities (0.1; 95% CI –0.2, 0.3). Maternal thyroid function test results were not associated with child cognitive test scores.

Conclusions: Newborn T₄ concentrations within a normal physiological reference range are not associated with maternal thyroid function and do not predict cognitive outcome in a population living in an iodine-sufficient area.