Study Fails To Support Routine Screening For Subclinical Hypothyroidism During Pregnancy Interview with:

Professor, Brian Casey, M.D. Gillette Professorship of Obstetrics and Gynecology UT Southwestern Medical Center

Dr. Casey

Professor Brian Casey, M.D.
Gillette Professorship of Obstetrics and Gynecology
UT Southwestern Medical Center What is the background for this study?
Response: For several decades now, subclinical thyroid disease, variously defined, has been associated with adverse pregnancy outcomes.  In 1999, two studies are responsible for increasing interest in subclinical thyroid disease during pregnancy because it was associated with impaired neuropsychological development in the fetus.  One study showed that children born to women with the highest TSH levels had lower IQ levels.  The other showed that children of women with isolated low free thyroid hormone levels performed worse on early psychomotor developmental tests. Together, these findings led several experts and professional organizations to recommend routine screening for and treatment of subclinical thyroid disease during pregnancy.

Our study was designed to determine whether screening for either of these two diagnoses and treatment with thyroid hormone replacement during pregnancy actually improved IQ in children at 5 years of age. What are the main findings?

Response: In each of the randomized, placebo-controlled treatment trials, thyroid hormone replacement during pregnancy did not improve IQ scores or other indices of cognitive function in children through 5 years of age.

Treatment also did not have an effect on behavior or measures of attention deficits or hyperactivity disorders.  Finally treatment did not improve pregnancy or neonatal outcomes. What should readers take away from your report?

Response: We embarked on this study because there was a burgeoning global movement that women with subclinical hypothyroidism or hypothyroxinemia carried the legacy of subnormal neurodevelopment in their children.

After more than a decade, including a comprehensive testing battery through 5 years of age, we can find no evidence that children of women with either subclinical hypothyroidism or isolated hypothyroxinemia during pregnancy benefit from thyroid hormone replacement, nor did we find any impact on pregnancy and neonatal outcomes.

Our study results, therefore, do not support routine thyroid screening to identify and treat pregnant women with either subclinical hypothyroidism or hypothyroxinemia.​ What recommendations do you have for future research as a result of this study?

Response: The results of our study, together with a previous study from the United Kingdom, are definitive evidence that screening for and treatment of pregnant women with subclinical thyroid hypofunction does not improve their children’s cognitive function or pregnancy outcomes. Thank you for your contribution to the community.


Treatment of Subclinical Hypothyroidism or Hypothyroxinemia in Pregnancy

Brian M. Casey, M.D., Elizabeth A. Thom, Ph.D., Alan M. Peaceman, M.D., Michael W. Varner, M.D., Yoram Sorokin, M.D., Deborah G. Hirtz, M.D., Uma M. Reddy, M.D., M.P.H., Ronald J. Wapner, M.D., John M. Thorp, Jr., M.D., George Saade, M.D., Alan T.N. Tita, M.D., Ph.D., Dwight J. Rouse, M.D., Baha Sibai, M.D., Jay D. Iams, M.D., Brian M. Mercer, M.D., Jorge Tolosa, M.D., Steve N. Caritis, M.D., and J. Peter VanDorsten, M.D., for the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal–Fetal Medicine Units Network*

N Engl J Med 2017; 376:815-825
March 2, 2017 DOI: 10.1056/NEJMoa1606205

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

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Last Updated on March 1, 2017 by Marie Benz MD FAAD