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Thyroid Deficiency in Pregnancy Affects Child IQ

Reuters News


Even a mild, symptom-free case of thyroid deficiency in a pregnant woman can affect her child's IQ scores years later, results of a study suggest.

Children aged 7 to 9 who had mothers with untreated hypothyroidism in pregnancy had IQ scores about 7 points lower than youngsters of women without such a deficiency, according to study results published in the August 19th issue of The New England Journal of Medicine.

The findings suggest that "routine prenatal or pre-pregnancy screening for thyroid deficiency needs to be considered," said lead study author Dr. James E. Haddow, of the Foundation for Blood Research in Scarborough, Maine, in an interview with Reuters Health.

In the report, the researchers note that for the first 12 weeks of pregnancy, before the unborn child's thyroid becomes active, "the mother is the sole source of thyroid hormones." Studies suggest that these hormones play a role in brain development.

Haddow and colleagues screened stored blood samples from more than 25,000 women who were pregnant between January 1987 and March 1990. They identified 62 women with thyroid deficiency, of whom 48 were not treated for hypothyroidism throughout pregnancy.

The investigators tested the neuropsychological development of the offspring of the 62 women and compared them with the children of 124 women without thyroid problems in pregnancy.

Between ages 7 and 9, children of the 48 mothers with untreated hypothyroidism scored 7 points lower, on average, on the Wechsler Intelligence Scale for Children. By comparison, IQ scores were similar between children of women whose hypothyroidism was treated during pregnancy and other youngsters.

Overall, compared with other children, the offspring of thyroid-deficient mothers had impaired school performance and lower scores on tests of attention, language, and visual-motor performance.

"Eleven years after the pregnancy under study, 64% of the untreated women and 4% of the matched control women had confirmed hypothyroidism," the investigators write, based on data from questionnaires they mailed. On average, hypothyroidism had been present for about 5 years in these women before being diagnosed, Haddow said.

"What we don't know from this study is whether you can effectively avoid the IQ problem in the child (by treating the mother's thyroid deficiency)," he said. However, because of the "minimal" risk of treating thyroid disease in pregnancy, the typical long delay in diagnosis and the simplicity of screening for thyroid deficiency, Haddow believes that widespread screening for hypothyroidism in pregnant women is "worth considering."

In an editorial, Dr. Robert D. Utiger notes that there are two potential causes of hypothyroidism in women: chronic autoimmune thyroiditis and iodine deficiency. He suggests that both causes likely play a role in thyroid deficiency in the US, where 15% of women of childbearing age had "overtly inadequate" intake of iodine between 1988 and 1994.

With this in mind, the editorialist notes that efforts to increase dietary iodine intake in the US should be the first step in any program to help prevent the adverse effects of hypothyroidism during pregnancy. "The beneficiaries would be not only pregnant women and their offspring, but everyone," Utiger concludes.



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