- Levothyroxine (Synthroid, Tirosint, Levoxyl) failed to improve live-birth rates in euthyroid women with preconception thyroid peroxidase (TPO) in a UK randomized controlled trial.
Why this matters
- TPO antibodies are associated with increased risk for miscarriage and preterm birth, and levothyroxine treatment had previously shown efficacy for preventing these outcomes in small trials.
- Pregnancy rate was not statistically different with levothyroxine vs placebo (56.6% vs 58.3%; relative risk [RR], 0.97; 95% CI, 0.88-1.07).
- Levothyroxine and placebo were associated with similar live-birth rates at ≥34 weeks (primary outcome; 37.4% vs 37.9%; RR, 0.97; P=.74).
- Levothyroxine and placebo were also associated with similar rates of miscarriage at
- 952 women with TPO antibodies and a history of miscarriage or infertility were randomly assigned to receive levothyroxine (50 μg once daily; n=476) or placebo (n=476) before conception through the end of pregnancy.
- Funding: UK NIHR Efficacy and Mechanism Evaluation Program.
- Dosing may not have been sufficient to observe an effect.