American Thyroid Association

American Thyroid Association

October 23, 2015
2 min read

Maternal free thyroxine levels may affect early brain development in offspring

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Adverse effects were found for early brain development in offspring of mothers with both low and high free thyroxine levels, according to recent study findings presented at the 15th International Thyroid Congress and 85th Annual Meeting of the American Thyroid Association.

“Although [thyroid-stimulating hormone] is considered the most important measurement to assess maternal thyroid function, we did not find any association of maternal TSH levels with child IQ or brain morphological outcomes,” Tim Korevaar, MD, MSc, of Erasmus Unviersity Medical Center in Rotterdam, Netherlands, told Endocrine Today. “Therefore, we believe it is important to assess gestational thyroid function by measuring both TSH and free T4 and to also monitor free T4 levels during treatment.”

Tim Korevaar

Tim Korevaar

Korevaar and colleagues evaluated 646 mother–child pairs from the Generation R Study to determine the relationship between maternal thyroid function with child IQ and brain morphology.

Child IQ (P = .0044), child gray matter volume (P = .0062) and cortex volume (P = .0011) all showed an inverted U-shape association with maternal free T4 levels.

Mean child IQ was 1.4 to 3.8 points lower for both low and high maternal free T4 concentrations.

Total white matter, corpus callosum or hippocampal volume were not associated with maternal free T4 and TSH was not associated with child IQ or brain MRI measurements.

“Both low and high maternal free T4 levels during pregnancy are associated with adverse effects on early brain development of the offspring,” Korevaar told Endocrine Today. “Our data suggests that changes in cerebral gray matter underlie previous results on the association of low maternal thyroid function with lower offspring IQ in human beings and that this does not depend on [human chorionic gonadotropin] stimulation or differences in child thyroid function postnatally. More importantly, our data also raise the concept that it is possible to overtreat patients receiving levothyroxine during pregnancy.”

Korevaar added that further research is needed to determine whether differences in thyroid function of the child could modify the associations of maternal thyroid function during pregnancy with child neurodevelopmental outcomes.

“Also, we are in need of a randomized controlled trial that includes women during early pregnancy and, if necessary, initiates treatment to normalize the [free] T4,” he said.

The findings also were published simultaneously in The Lancet Diabetes & Amber Cox


Korevaar TI, et al. Oral 67. Presented at: 15th International Thyroid Congress and 85th Annual Meeting of the American Thyroid Association (ITC/ATA); Oct. 18-23, 2015; Lake Buena Vista, Fla.

Korevaar TI, et al. Lancet Diabetes Endocrinol. 2015;doi:10.1016/S2213-8587(15)00327-7.

Disclosure: Korevaar reports no relevant financial disclosures.