Although levothyroxine (LT4) does not decrease the chances of preterm delivery among pregnant hypothyroid women who are negative for thyroid peroxidase antibody (SCH-TPOAb), the therapy may hold benefit for women with a thyrotropin cutoff value of ≥4.0 mIU/L, according to findings from a single-blind, randomized clinical trial published in the Journal of Clinical Endocrinology & Metabolism.

Using the Tehran Thyroid and Pregnancy study as a framework, researchers evaluated the utility of LT4 therapy with a thyrotropin cut point of 2.5 mIU/L for reducing preterm delivery in SCH-TPOAb women (n=366) and euthyroid TPOAb control patients (n=1028). A total of 2 SCH-TPOAb subgroups were created: Women were randomly assigned either to a morning dose of 1 μg/kg/day LT4 (n=183) or to no treatment (n=183).

When investigators used the thyrotropin cutoff of 2.5 mIU/L, they found no difference between the 2 SCH-TPOAb subgroups with regard to the rate of preterm deliveries (risk ratio [RR], 0.86; 95% CI, 0.47-1.55; P =.61). A log-binomial model analysis using a cutoff point of 4.0 mIU/L, however, did correlate with a lower preterm delivery rate among those treated with LT4 vs no treatment (RR, 0.38; 95% CI, 0.15-0.98; P =.04).

The researchers note that they were unable to obtain clinically meaningful results regarding miscarriage rates because of nontimely patient referral. in addition, the investigators did not measure antithyroglobulin antibodies, limiting the ability to sufficiently distinguish patients with thyroid autoimmunity.

According to the investigators, treatment with LT4 did not affect neonatal admission rates, in part “due to the higher gestational age of newborns at the time of delivery or the exclusion of TPOAb+ women who are more likely to suffer perinatal complications, irrespective of thyroid hypofunction mechanisms.”

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Reference

Nazarpour S, Ramezani Tehrani F, Simbar M, et al. Effects of Levothyroxine on pregnant women with subclinical hypothyroidism, negative for thyroid peroxidase antibodies [published online November 6, 2017]. J Clin Endocrinol. doi:10.1210/jc.2017-01850