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Health & Pregnancy

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Underactive Thyroid in Pregnancy Can Lead to Problems in Children

WebMD Health News

Dec. 9, 1999 (New York) -- A recent study showing that even a mildly underactive thyroid gland in a pregnant woman can affect her child's brain development has led major physicians' groups to call for closer monitoring of thyroid hormone levels during pregnancy. In a statement published in the November/December issue of the journal Endocrine Practice, the American Association of Clinical Endocrinologists makes six recommendations for clinicians to consider when caring for women of child-bearing age.

These recommendations come several months after a major study published in The New England Journal of Medicine showed that an underactive thyroid, or hypothyroidism, in which thyroid hormone levels are so mildly depressed that the person shows no symptoms, has profound effects on children. In that study, James Haddow, MD, and colleagues from the Foundation for Blood Research in Scarborough, Maine, found that school-age children whose mothers were hypothyroid during pregnancy had lower IQ scores than children whose mothers were not hypothyroid during pregnancy. Overall, 19% of children of hypothyroid mothers had scores of 85 or lower compared with just 5% of children born to women with normal thyroids. The average IQ score is 100.

Both animal and human studies have shown that thyroid hormones are crucial to brain development. In the new position statement, American Association of Clinical Endocrinologists officers including president Richard A. Dickey, MD, recommend preconception thyroid hormone testing for all women considering pregnancy so that hypothyroidism can be diagnosed early and treated prior to pregnancy. The recommendations also state that routine testing of the level of thyroid stimulation hormone, known as a TSH or thyrotropin test, early in pregnancy is "reasonable but should be left to the judgment of the physician, in consultation with the patient."

A co-author of the study on which the new recommendations are based tells WebMD that the suggestions for clinicians are reasonable and close to what the authors had in mind. "No one really knows what the right thing to do is," says Walter C. Allan, MD. "When you start talking about population-wide screening for hypothyroidism, you get into issues of cost. But women who are of child-bearing years should be screened with a simple TSH test and if they do indeed have an elevated TSH, that should definitely be considered during the pregnancy and they should be treated," Allan tells WebMD. TSH elevation acts to depress the release of hormones from the thyroid gland, thus leading to hypothyroidism.

He says his group and others think the next step should be to begin thyroid hormone screening in young women of child-bearing age. A significant percentage will show mild hypothyroidism. These women should be treated and monitored further during pregnancy where the thyroid hormone levels are known to decrease. Medication adjustments may be needed during pregnancy as the hormone levels change "We still need to prove that the model that people are advocating will work and will be cost effective," says Allan. "Thyroid treatment is inexpensive and not harmful for pregnant women. There are very few causes of low IQ that we can do anything about. This is a pretty simple thing to do something about."

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