Thyroid hormones supplementation 50 mcg daily did not improve pregnancy outcomes in women with Hashimoto's thyroiditis in the presence of normal thyroid function. Hashimoto’s thyroiditis was confirmed by elevated TPO antibodies at study entry. About 1,000 pregnant women were followed through full term.
This is an important study as it defies the current medical opinion of poorer pregnancy outcomes in euthyroid Hashimoto's thyroiditis.
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Thyroid peroxidase antibodies are associated with an increased risk of miscarriage and preterm birth, even when thyroid function is normal.
Small trials indicate that the use of levothyroxine could reduce the incidence of such adverse outcomes.
We conducted a double-blind, placebo-controlled trial to investigate whether levothyroxine treatment would increase live-birth rates among euthyroid women who had thyroid peroxidase antibodies and a history of miscarriage or infertility.
A total of 19,585 women from 49 hospitals in the United Kingdom underwent testing for thyroid peroxidase antibodies and thyroid function.
We randomly assigned 952 women to receive either LEVO 50 μg once daily (476 women) or placebo (476 women) before conception through the end of pregnancy.
Primary outcome was live birth after at least 34 weeks of gestation.
The follow-up rate for the primary outcome was 98.7% (940 of 952 women).
A total of 266 of 470 women in the levothyroxine group (56.6%) and 274 of 470 women in the placebo group (58.3%) became pregnant.
The live-birth rate was 37.4% (176 of 470 women) in the levothyroxine group and 37.9% (178 of 470 women) in the placebo group (RR, 0.97; p=0.74)
There were no significant between-group differences in other pregnancy outcomes, including pregnancy loss or preterm birth, or in neonatal outcomes.
Serious adverse events occurred in 5.9% of women in the levothyroxine group and 3.8% in the placebo group (P=0.14).
The use of levothyroxine in euthyroid women with thyroid peroxidase antibodies did not result in a higher rate of live births than placebo.