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Treatment for hypothyroidism during pregnancy may not improve cognitive function in children
Lazarus JH. N Engl J Med. 2012;366:493-501.
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Children of women who were treated for hypothyroidism during pregnancy had similar IQ results at age 3 years as children of women who were not treated, according to recent results.
The trial was conducted to build on previous evidence that children born to women with low thyroid hormone levels have decreased cognitive function.
Eligible participants were pregnant women at a gestation of 15 weeks 6 days or less. These women provided blood samples for measurement of thyrotropin and free thyroxine.
There were two arms of the study: the screening group, in which measurements were obtained immediately, or a control group, in which serum was stored and measurements were obtained shortly after delivery.
Positive screening results were defined as thyrotropin levels higher than the 97.5th percentile, free T4 levels lower than the 2.5th percentile or both.
Women who received positive test results were assigned 150 mcg levothyroxine per day.
The primary outcome measure was the IQ of the child at 3 years among children of women with positive results.
The median gestational age was 12 weeks 3 days. Blood samples were provided by 21,846 women.
The final analysis included 390 women in the screening group and 404 in the control group, all of whom had received positive test results.
Levothyroxine treatment was initiated at a median gestational age of 13 weeks 3 days. The target thyrotropin level was 0.1 mIU/L to 1 mIU/L, and adjustments were made during treatment to reach this level.
The mean IQ score among children of women who tested positive in the screening group was 99.2 vs. 100 in the control group (difference of 0.8; 95% CI, -1.1 to 2.6).
The ratio of children with an IQ of less than 85 was 12.1% in the screening group vs. 14.1% in the control group (difference of 2.1 percentage points; 95% CI, -2.6 to 6.7). On-treatment analysis results were similar.
“Antenatal screening … and maternal treatment for hypothyroidism did not result in improved cognitive function in children at 3 years of age,” the researchers said.
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