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Because the fetus does not make thyroid hormone until the second trimester of pregnancy, investigators have suspected that maternal hypothyroidism might impair offsprings' intellectual function. These investigators measured serum thyrotropin (TSH) during the second trimester in more than 25,000 pregnant women in Maine. Seven to nine years later, investigators contacted the 47 women with TSH levels at or above the 99.7 percentile, 15 women with TSH values between the 98 and 99.6 percentiles, and 124 matched controls with normal TSH levels. Their children's intelligence, attention, language, reading ability, and school and visual-motor performance were assessed. None of the women's children had been diagnosed with hypothyroidism during routin…