Background: Thyroid peroxidase antibodies are associated with increased risk of miscarriage and preterm birth, even when thyroid function is normal. Small trials indicate levothyroxine could reduce such adverse outcomes.
Methods: We conducted a double-blind, placebo-controlled trial to investigate whether levothyroxine treatment would increase live birth rates among euthyroid women with thyroid peroxidase antibodies and a history of miscarriage or infertility. We randomly assigned women to receive 50 mcg daily of levothyroxine or placebo, commenced preconception and continued until the end of pregnancy. The primary outcome was live birth 334 weeks gestation.
Results: We tested 19,585 women for thyroid peroxidase antibodies and thyroid function across 49 hospitals in the United Kingdom. A total of 952 women were randomly assigned to receive either levothyroxine (476) or placebo (476). The follow-up rate for the primary outcome was 98.7% (940/952). A pregnancy was achieved in 266/470 (56.6%) in the levothyroxine group and 274/470 (58.3%) in the placebo group. The live birth rate in the levothyroxine group was 37.4% (176/470) versus 37.9% (178/470) in the placebo group (relative risk, 0.97; 95% confidence interval [CI], 0.83 to 1.14, P=0.74; absolute risk difference, −0.4%; 95% CI, −6.6% to 5.8%). There were no significant differences in other pregnancy outcomes, including the rates of pregnancy loss, preterm birth, or in neonatal outcomes. Serious adverse events occurred in 6% of women in the levothyroxine group and 4% in the placebo group (P=0.14).
Conclusion: Treatment with levothyroxine in euthyroid women with thyroid peroxidase antibodies did not increase the rate of live births.
18 - 21 May 2019
European Society of Endocrinology