The treated women had monthly measurements of TSH and FT4. On the basis of the results of these measurements, doses were adjusted, with sham adjustments in the placebo groups. The goal of the levothroxine therapy was a TSH of 0.1 to 2.5 mU/L with maximum dose of 200 μg. For the hypothyroxinemia trial, the goal was FT4 between 0.86 and 1.90 ng/dl. The primary outcome was the full-scale IQ at age 5 years.
From October 2006 to October 2009, a total of 97,228 pregnant women underwent thyroid screening; 3057 had subclinical hypothyroidism; 800 of these women were eligible and consented to participate. A total of 677 of them underwent randomization for the study. Hypothyroxinemia was diagnosed in 805 women, of whom 632 were eligible and 526 underwent randomization. In the subclinical hypothyroidism trial, randomization occurred before 17 weeks and 93% of the L-T4-treated group achieved a TSH between 0.1 and 2.5 mU/L by 21 weeks. In the hypothyroxinemia trial, randomization occurred at 18 weeks, and 83% of women treated with levothyroxine achieved an FT4 between 0.86 and 1.90 ng/dl by 23 weeks.
In the subclinical hypothyroidism trial, the average IQ at 5 years was 97 in the levothyroxine treated group and 94 placebo group. In the hypothyroxinemia trial, the average IQ at 5 years was 94 in the levothyroxine treated group and 91 in the placebo group. None of these differences were significant. Further, there were no differences in adverse pregnancy events or outcomes between the levothyroxine treated and placebo groups in either trial.
WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that levothyroxine therapy for subclinical hypothyroidism or hypothyroxinemia diagnosed during pregnancy beginning at an average of 17 to 19 weeks of pregnancy had no effect on pregnancy outcomes or on brain development in children through 5 years of age than no treatment for these conditions. Because treatment has no effect, these data suggest that screening pregnant women for subclinical hypothyroidism or hypothyroxinemia is not helpful.
— Alan P. Farwell, MD, FACE
ATA THYROID BROCHURE LINKS
Thyroid and Pregnancy: https://www.thyroid.org/ thyroid-disease-pregnancy/
Thyroid Function Tests: https://www.thyroid.org/ thyroid-function-tests/
Hypothyroidism: https://www.thyroid.org/ hypothyroidism/