(HealthDay News) — Treatment for subclinical hypothyroidism or hypothyroxinemia before 20 weeks of gestation is not associated with better cognitive outcomes in children, according to a study published in the March 2 issue of the New England Journal of Medicine.

Brian M. Casey, M.D., from the University of Texas Southwestern Medical Center in Dallas, and colleagues screened women with a singleton pregnancy for subclinical hypothyroidism and for hypothyroxinemia before 20 weeks of gestation. Women were randomized to levothyroxine or placebo in separate trials: 677 women with subclinical hypothyroidism underwent randomization at a mean of 16.7 weeks of gestation and 526 with hypothyroxinemia were randomized at a mean of 17.8 weeks of gestation.

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The researchers found that the median IQ score of children at age 5 years was 97 and 94 in the levothyroxine and placebo groups, respectively, in the subclinical hypothyroidism trial (P = 0.71), and 94 and 91, respectively, in the hypothyroxinemia trial (P = 0.30). IQ scores were missing for 4 percent of children in each trial. No significant between-group differences were seen in either trial for any neurocognitive or pregnancy outcomes or for adverse event incidence.

“Treatment for subclinical hypothyroidism or hypothyroxinemia beginning between 8 and 20 weeks of gestation did not result in significantly better cognitive outcomes in children through 5 years of age than no treatment for those conditions,” the authors write.

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