Children whose mothers were treated for subclinical hypothyroidism or hypothyroxinemia during pregnancy showed similar cognitive performance through age 5 years to those whose mothers received placebo, according to a pair of studies involving > 1,200 women. Participants were screened before 20 weeks of gestation for hypothyroidism (n=677) and hypothyroxinemia (n=526). In separate trials, women were randomized to receive levothyroxine or placebo. Thyroid function was observed monthly and children were examined for developmental and behavioral issues yearly for 5 years, and IQ score was recorded. Among the results:

• In the hypothyroidism trial, median IQ was 97 in children whose mothers were treated with levothyroxine vs 94 in the placebo group.
• In the hypothyroxinemia trial, median IQ in the treatment and placebo groups were 94 and 91, respectively.
• There were no significant between-group neurocognitive or pregnancy outcome differences in either trial.
• Adverse events were low in both groups in both trials.