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Levothyroxine fails to decrease pregnancy loss in women with thyroid antibody positivity
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NEW ORLEANS — Euthyroid women with thyroid antibody positivity prescribed levothyroxine before and during pregnancy were no more likely to experience a live birth at 34 weeks of gestation than similar women assigned to placebo treatment, according to findings presented at the Endocrine Society Annual Meeting.
“For women who are positive for thyroid antibodies but have a normal thyroid function, giving them levothyroxine started before pregnancy and continued throughout pregnancy does not increase their chances of having a live baby,” Rima Dhillon-Smith, PhD, MRCOG, MBChB, a specialist registrar in obstetrics and gynecology and academic clinical lecturer in early pregnancy and reproductive medicine at the University of Birmingham, United Kingdom, told Endocrine Today. “Levothyroxine should not be provided to women with thyroid antibodies who have a normal thyroid function and are trying for a pregnancy because it has no proven benefit.”
In the double-blind, placebo-controlled TABLET trial, Dhillon-Smith and colleagues analyzed data from 952 euthyroid women (mean age, 33 years) with thyroid peroxidase antibody positivity, recruited from 49 U.K. hospitals, who experienced at least one miscarriage or were undergoing fertility treatment. The women were randomly assigned to receive 50 µg once-daily oral levothyroxine (n = 476) or placebo (n = 476) before conception through the end of pregnancy. Once pregnant, women attended three trial visits and underwent thyroid function testing at 6 to 8 weeks, 16 to 18 weeks and 28 weeks.
The findings were simultaneously published in The New England Journal of Medicine.
Within the cohort, 266 women in the levothyroxine group (56.6%) and 274 women in the placebo group (58.3%) became pregnant.
The primary outcome — live birth after at least 34 weeks of gestation — occurred in 37.4% of the levothyroxine group vs. 37.9% of the placebo group, for a relative risk of 0.97 (95% CI, 0.83-1.14).
The researchers observed no between-group differences in pregnancy outcomes, including pregnancy loss, preterm birth rates or neonatal outcomes.
Women in the levothyroxine group experienced more adverse events compared with women assigned placebo (5.9% vs. 3.8%; P = .14), including a higher rate of preeclampsia and gestational diabetes, Dhillon-Smith said.
The percentages of women who discontinued therapy due to abnormal results on thyroid function tests were similar in the levothyroxine and placebo groups, at 9.8% and 9.6%, respectively.
“Unfortunately, much to our dismay, after screening nearly 20,000 people, there was absolutely no difference at all between the two groups,” Dhillon-Smith said. “Also, sadly, no difference in any of the secondary outcomes.”
In a priori subgroup analysis, the results persisted for women with higher TSH values above 2.5, Dhillon-Smith said.
“The two take-home messages are, firstly, we need to stop prescribing [levothyroxine] for this population,” Dhillon-Smith said. “It doesn’t have a benefit and we need to [increase awareness] that there is no benefit.”
The findings also call into question recommendations to test thyroid hormone levels in pregnant women, Dhillon-Smith said.
“One of the prerequisites for a screening test is that you need to have a treatment or intervention which modifies the outcome and, at present, for this population, we don’t have that,” Dhillon-Smith said. “Are we just generating anxiety rather than helping them?” – by Regina Schaffer
References:
Dhillon-Smith RK. A randomized trial of preconception levothyroxine in euthyroid women with thyroid peroxidase antibodies. Presented at: The Endocrine Society Annual Meeting; March 23-26, 2019; New Orleans.
Dhillon-Smith RK, et al. N Eng J Med. 2019; doi:10.1056/NEJMoa1812537.
Disclosure: Dhillon-Smith reports no relevant financial disclosures.