Dhillon-Smith RK, et al. - Among euthyroid women who had thyroid peroxidase antibodies and a history of miscarriage or infertility, researchers ascertained if levothyroxine treatment would increase live-birth rates. In women with thyroid peroxidase antibodies, the use of levothyroxine did not result in a higher rate of live births than placebo.

Methods

• It was a double-blind, placebo-controlled trial.
• A total of 19,585 women were tested for thyroid peroxidase antibodies and thyroid function from 49 hospitals in the United Kingdom.
• For this trial, 952 women were randomly assigned to receive either 50 μg once daily of levothyroxine (476 women) or placebo (476 women) before conception through the end of pregnancy.
• Live birth after at least 34 weeks of gestation was the primary outcome.

Results

• The primary outcome follow-up rate was 98.7% (940 of 952 women).
• A total of 266 of 470 women in the group of levothyroxine (56.6%) and 274 of 470 women in the group of placebo (58.3%) were pregnant.
• Investigators found that the live-birth rate was 37.4% (176 of 470 women) in the group of levothyroxine and 37.9% (178 of 470 women) in the group of placebo (relative risk, 0.97; 95% confidence interval [CI], 0.83 to 1.14, P=0.74; absolute difference, -0.4 percentage points; 95% CI, -6.6 to 5.8). 
• They found no significant between-group differences in other pregnancy outcomes, including pregnancy loss or preterm birth, or in neonatal outcomes.
• In 5.9% of women in the levothyroxine group and 3.8% in the placebo group (P=0.14), serious adverse events occurred.