While, normal thyroid function is vital for healthy brain development, it has been suggested in earlier studies that even mild maternal hypothyroidism during pregnancy may have adverse effect on child cognitive development.
In the Project Viva, a team of researchers led by Dr. Emily Oken of Harvard Medical School and Harvard Pilgrim Health Care, studied 500 children born 1999-2003 to evaluate the relationship between thyroxine levels in newborns, first trimester maternal thyroid function, and childhood cognition.
In the first place, scientists tested mothers' thyroid stimulating hormone, thyroxine, and thyroid peroxidase antibody levels at an average of 10.2 weeks gestation and later measured newborns' thyroxine levels from whole blood samples after birth.
Later, they performed cognitive testing when the infants were six months old using the visual recognition memory test, a measure of infant cognition that can predict later childhood IQ and specific abilities in perceptual speed, language, and memory.
At the age of three years, the children were tested with the Peabody Picture Vocabulary Test a measure of verbal ability or scholastic aptitude, and the Wide Range Assessment of Visual Motor Ability , which evaluates visual-spatial analysis, visual-motor ability, and fine motor skills.
They found no correlation between newborn thyroxine levels and maternal thyroxine, TSH or TPO antibody levels.
When they performed multivariable linear regression analysis, it was found that higher thyroxine was associated with slightly poorer scores on the VRM among infants at six months, but not with scores at age three on either the PPVT or the WRAVMA; maternal thyroid function was not found to be related to child cognitive test scores.
"In this sample from an iodine sufficient area, first-trimester maternal thyroid function does not appear to affect a newborn's thyroid function at birth, nor does lower neonatal thyroid function within the normal range impact a child's cognition," said one of the co-authors of the study.
He added: "These findings were unexpected. We look forward to the results of trials currently ongoing in the U.S. and Europe to better elucidate the relationship between mild maternal hypothyroidism and child cognition."
The study will be presented at the 79th Annual Meeting of the American Thyroid Association (ATA) in Chicago, IL.