Thyroid autoantibodies increase risk for miscarriage, preterm birth

In women with normal thyroid function, the presence of thyroid autoantibodies is associated with a more than tripled risk for miscarriage and a doubled risk for preterm birth, according to the findings of a systematic review and meta-analysis of the published literature.

Researchers from England included 31 studies involving 12,126 women. Among the 19 cohort studies included, they calculated an odds ratio (OR) of 3.90 for miscarriage in the presence of thyroid autoantibodies (95% confidence interval [CI], 2.48-6.12; P<0.001). Among the 12 case-control studies included, researchers calculated an OR for miscarriage of 1.80 (95% CI, 1.25-2.60; P=0.002). The likelihood of preterm birth in the presence of thyroid antibodies was 2.07 (95% CI, 1.17-3.68; P=0.01). All studies looking at this association were cohort studies. Two randomized studies looked at treatment with levothyroxine. Treating women with thyroid antibodies with levothyroxine reduced the risk for miscarriage by 52% (relative risk [RR], 0.48; 95% CI, 0.25-0.92; P=0.03) and the rate of preterm birth by 69% (RR, 0.31; 95% CI, 0.11-0.90).

Thyroid autoantibodies are highly prevalent in women of reproductive age. The studies included in this meta-analysis reported a prevalence of between 5.4% and 31%. The researchers could not account for the increase in miscarriage rate in the presence of thyroid autoantibodies with confounding factors such as a difference in age.

Thangaratinam S, Tan A, Knox E, Kilby MD, Franklyn J, Coomarasamy A. Association between thyroid autoantibodies and miscarriage and preterm birth: meta-analysis of evidence. BMJ. 2011;342:d2616.