Cause of Visual Problems Among Children of Hypothyroid Mothers Found

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 presented 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 on thyroid disease and pregnancy, visit http://www.thyroid.org.
The American Thyroid Association (ATA) is the lead organization in promoting thyroid health and understanding thyroid biology. The ATA values scientific inquiry, clinical excellence, public service, education, collaboration, and collegiality.

A non-profit medical society founded in 1923, the ATA fulfills its mission through supporting excellence and innovation in research, clinical care, education, and public health. ATA members are physicians and scientists who work to enhance the understanding of thyroid physiology and pathophysiology, improve the diagnosis and treatment of thyroid diseases, and promote the education of physicians, patients, and the public about thyroid disorders.
Thyroid diseases are among the most common disorders of the endocrine system, affecting almost 13 million Americans alone. The ATA has extensive online information for patients on thyroid disease (in English and Spanish) serving the clinician as a resource for patients and the public who look for reliable information on the internet. To further benefit patients, the ATA Alliance for Patient Education was formed in 2002 to offer an exchange of information between the ATA and four patient groups: Thyroid Foundation of America, ThyCa: Thyroid Cancer Survivors, Inc.; the Light of Life Foundation, and the National Graves’ Disease Foundation. A public forum is held each year in conjunction with the ATA annual meeting.

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American Thyroid Association Released: Thu 04-Oct-2007, 09:00 ET