In women with unexplained recurrent pregnancy loss, thyroid peroxidase antibody (TPOAb) positivity is associated with a reduced live birth rate, according to study results published in Thyroid. Thyroxine (T4) replacement treatment, however, may improve the odds of live birth.

Existing evidence suggests that thyroid autoimmunity may be associated with reproductive challenges such as pregnancy loss, but other research has questioned the association between thyroid antibody positivity and miscarriage. The current study included women with recurrent pregnancy loss treated at a tertiary referral center at Copenhagen University Hospital in Denmark from 2011 to 2017 (n=825). The researchers defined unexplained recurrent pregnancy loss as ≥3 consecutive losses or 2 second trimester losses/still births not attributable to antiphospholipid syndrome, parental chromosome abnormality, or uterus malformation.

Women were screened for thyrotropin and TPOAbs (TPOAb positivity ≥60 kIU/L) at baseline. The researchers performed logistic regression analyses that adjusted for maternal age at referral, thyrotropin level, number of previous losses, body mass index, smoking status, pregnancy achieved by assisted reproductive technology, and T4 treatment.

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Of 825 women with 3246 previous pregnancy losses before referral, 16.8% (n=139) were found to be TPOAb positive. TPOAb positivity was not associated with the number of previous losses (P =.41; odds ratio [OR] adjusted for maternal age, 0.95; 95% CI, 0.82-1.09; P =.44) or with the number of previous pregnancies (P =.51; OR adjusted for maternal age, 0.96; 95% CI, 0.86-1.06; P =.40).

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In 454 women who had a first pregnancy after referral, the live birth rate was 62.8% (n=285). The researchers found that 17.2% (n=78) were TPOAb positive and that TPOAb positivity was associated with a significantly reduced live birth rate compared with TPOAb negativity (51.3% vs 65.2%, respectively; P =.02; adjusted OR, 0.2; 95% CI, 0.1-0.6; P =.001).

The researchers noted that treatment with T4 was linked to an increased live birth rate (adjusted OR, 3.7; 95% CI, 1.4-9.8; P =.007). TPOAb-positive women who received T4 had a similar live birth rate compared with TPOAb-negative women who did not receive T4 (P =.70).

“Although the findings need confirmation from placebo-controlled trials, the present results speak in favor of screening for thyroid autoantibodies in this patient group,” the researchers wrote. “A close collaboration between fertility doctors and endocrinologists is pivotal in insuring the best possible management of these women, both before and during pregnancy.”

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Bliddal S, Feldt-Rasmussen U, Rasmussen AK, et al. Thyroid peroxidase antibodies and prospective live birth rate: a cohort study of women with recurrent pregnancy loss [published online September 24, 2019]. Thyroid. doi:10.1089/thy.2019.0077