ATA News Release 2007

High TSH Levels May Cause Infants of Mothers With Under-active Thyroid To Have Visual Contrasting Problems

Oct. 4, 2007, 9:15 a.m. EDT —Children of women with hypothyroidism—an under-active thyroid—who had elevated thyroid stimulating hormone (TSH) in the first and second trimesters of pregnancy, had a significantly reduced ability to see visual contrasts, compared to women with hypothyroidism with normal TSH levels during the first two trimesters, and pregnant women with normal thyroid levels, according to a new study being presented on Thursday, Oct. 4, at the 78th Annual Meeting of the American Thyroid Association (ATA) in New York. Adequate contrast sensitivity is an important ability for reading, viewing information of low contrast such as maps, and visuospatial ability in general.

The study shows that visual processing problems among infants of women with hypothyroidism were directly correlated with the mothers’ high level of TSH.  These findings suggest that thyroid hormone is critical in early pregnancy for normal development of visual processing abilities.

A previous study showed that infants born to women who had hypothyroidism diagnosed prior to or during pregnancy had reduced ability to see visual contrasts and that the severity of their deficit was related to how hypothyroid their mothers were during the pregnancy.  This research was based on an electrophysiological task where children saw bars that swept from low to high levels of contrast at a slow speed. 

Researchers in this study wanted to expand on the previous study to include higher speeds of stimulus presentation, since they are thought to invoke a structure in the brain that is sensitive to rapidly moving stimuli. As the presentation speed increased, so did the response of a specific cell type in the thalamus, which signals contrasts in brightness.

The study involved 36 six-month-old infants born to hypothyroid women treated with levothyroxine, who were diagnosed prior to or during their pregnancies, and 22 control infants.

“The study shows the importance of adequate thyroid hormone levels for women in the early stages of their pregnancy for the neurological development of the fetus,” said Joanne F. Rovet, M.D., lead author of the study and a Senior Scientist at The Hospital for Sick Children in Toronto and Professor of Pediatrics at University of Toronto. “Mothers with pre-existing hypothyroidism should be monitored closely during their pregnancy to ensure that their hormone levels are adequately adjusted.”

For more information, please contact the ATA at thyroid@thyroid.org.