Initiation of levothyroxine before conception and throughout pregnancy did not result in a higher rate of live births than placebo in euthyroid women with thyroid peroxidase antibodies and a history of miscarriage, according to study data presented at the Endocrine Society’s annual meeting, ENDO 2019, held March 23 to 26 in New Orleans, Louisiana.1,2

Previous trials indicated that the use of levothyroxine could reduce the incidence of miscarriage, one of the most common complications of pregnancy. Of 19,556 women screened for the study, 1420 met inclusion criteria, of which 952 consented to participate. Women were excluded if they were receiving treatment for a thyroid disorder, had cardiac disease, or were receiving amiodarone or lithium.

In this double-blind, placebo controlled trial, researchers randomly assigned 952 women to receive either 50 mcg once daily of levothyroxine (n = 476) or placebo (n = 476) before conception through the end of pregnancy.  The primary outcome was live birth after at least 34 weeks of gestation.

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The follow-up rate for the primary outcome was 98.7% (940/952). In the levothyroxine treatment group, a pregnancy was achieved in 56.6% of the population, with a live birth rate of 37.4%. In the placebo group, pregnancy was achieved in 37.9% of the population, with a live birth rate of 37.9% (relative risk, 0.97; 95% CI, 0.83-1.14, P =.74; absolute risk difference, -0.4%; 95% CI, -6.6% to 5.8%). Serious adverse events occurred in 6% of women in the levothyroxine group and 4% in the placebo group (P =.14).


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There were no significant differences in other pregnancy outcomes, including the rates of preterm birth, pregnancy loss, or neonatal outcomes.

Ultimately, this study was much larger than previous studies, and was not restricted to a single population. Researchers noted, “It was anticipated that broadening of the inclusion criteria to women with infertility might result in a decreased rate of live births and affect the power of the trial. However, the 95% confidence interval for the primary outcome rules out a clinically meaningful benefit, and therefore a potential reduction in power does not affect our inferences.”1

Please refer to reference for a complete list of authors’ disclosures.

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References

1. Dhillon-Smith R, Middleton L, Sunner K, et.al. Levothyroixine in women with thyroid peroxidase antibodies before conception [published online March 23, 2019]. NEJM. doi:10.1056/NEJMoa1812537

2. Dhillon-Smith R, Middleton L, Sunner K, et.al. A randomized trial of preconception levothyroxine in euthyroid women with thyroid peroxidase antibodies. Presented at: ENDO 2019; March 23-26, 2019; New Orleans, LA. Abstract OR11-1.