It is already known to doctors that low thyroid hormone levels during pregnancy have something to do with lower IQ scores of kids and other risks to the foetus. However, a new study finds that high thyroid hormone levels during early pregnancy may significantly lower the baby’s IQ later in childhood as well. The results suggest that the common treatment for pregnant women who have mild thyroid hormone deficiency may bring unexpected risks to the developing of baby’s brain.
According to current evidence, treatment guidelines from the American Thyroid Association in 2011 and the Endocrine Society in 2012 recommend medical treatment of pregnant women with subclinical hypothyroidism. It is a mild form of thyroid issue in which there is an increased amount of thyroid-stimulating hormone (TSH). TSH, meanwhile, is the substance that stimulates the production of the thyroid hormones T3 and T4, as well as keeps them in proper amount. T3 and T4 control how your body uses energy. The scientist said, there is agreement on treating the issue since the potential benefits that the treatment of subclinical hypothyroidism brings is generally believed weigh more than the potential risks of overtreatment. However, no evidence in humans, as a matter of fact, that moderate degree increased levels of thyroid hormone could also have a bad effect on baby until now.
The scientists evaluated the data of 3,839 mother-child pairs. Mothers had blood test to measure their TSH and free T4（the active form of T4）between weeks 9 and 18. After the children were born, they received an I Q test on nonverbal performance tasks between the age of 5 and 8 years.
The researchers found that the average nonverbal IQ of the children significantly decreased 2.1 to 3.8 points, which is below the average of the reference group (those with free T4 levels in the middle of the range) when the mothers’ free T4 level was at or above the normal range.
Since the methods to measure free T4 differ from countries and hospitals, percentiles were calculated. The researcher said that the important point in this study is that both low and high TSH levels were linked with lower child IQ levels, which was obvious during the entire range of maternal free T4 levels. There was no independent connection found between women’s TSH level and changes in child IQ.
The researcher said, according to European and American surveys, there is a rapid increasing in the proportion of pregnant women with mild thyroid dysfunction who receive thyroid hormone supplementation. Thyroid hormone supplementation during pregnancy may bring the risk of overtreatment, and even treatment to a high-normal level on thyroid function tests early in pregnancy may not utterly eliminate the risks to the child. Therefore, physicians are advised to supplement with care.