High-normal thyroid hormone level in pregnancy may damage fetal brain development

http://www.eurekalert.org/pub_releases/2015-03/tes-hth030515.php

Public Release: 6-Mar-2015
The Endocrine Society

A new study finds that not only low but also high maternal thyroid hormone levels during early pregnancy may significantly lower the infant's IQ later in childhood. The study results, which will be presented Thursday at the Endocrine Society's 97th annual meeting in San Diego, suggest that the common practice of treating pregnant women who have mild thyroid hormone deficiency may pose unexpected risks to the developing baby's brain.

Doctors already know that low thyroid hormone levels in pregnant women are linked to lower child IQ scores as well as other risks to the fetus. Based on 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. In this mild form of thyroid disease, there is an increased amount of thyroid-stimulating hormone (TSH), the substance that spurs production of and maintains adequate amounts of the thyroid hormones, T3 and T4, which control how your body uses energy.

•••••

"The proportion of pregnant women with mild thyroid dysfunction who receive thyroid hormone supplementation is rapidly increasing, according to European and American surveys," Korevaar said. "Thyroid hormone supplementation during pregnancy may come with the risk of overtreatment, and even treatment to a high-normal level on thyroid function tests early in pregnancy may not be without risks to the child. We advise physicians to supplement with care."