Levothyroxine to increase live births in euthyroid women with thyroid antibodies trying to conceive: the TABLET RCT

Thyroid autoantibodies, specifically thyroid peroxidase antibodies, have been associated with miscarriage and pre-term birth in women with a normal thyroid function. Small randomised controlled trials have found that treatment with levothyroxine may reduce such adverse outcomes in pregnancy. The Thyroid AntiBodies and LEvoThyroxine (TABLET) trial was conducted to explore the effects of levothyroxine in euthyroid women with thyroid peroxidase antibodies. This was a randomised, double-blind, placebo-controlled, multicentre study conducted in 49 hospitals across the UK between 2011 and 2016. Euthyroid women who tested positive for thyroid peroxidase antibodies, were aged between 16 and 41 years and were trying to conceive either naturally or through assisted conception were eligible. Participants were randomised to levothyroxine at a dose of 50 mcg daily or placebo. The primary outcome was live birth at >= 34 completed weeks of gestation. Of the 19,556 women screened, 1420 were eligible and 952 were randomised. The live birth rate was 37% in the levothyroxine group and 38% in the placebo group (relative risk 0.97, 95% CI 0.83 to 1.14; p = 0.74). Levothyroxine therapy in a dose of 50 mcg per day does not improve live birth rate in euthyroid women with thyroid peroxidase antibodies.