Thyroid antibodies and risk of preterm delivery: a meta-analysis of prospective cohort studies

Background: Observational studies suggest possible associations between thyroid antibodies and risk of preterm delivery. However, whether thyroid antibodies are risk factors of preterm labor remains controversial. Our goal was to evaluate the associations between thyroid antibodies and risk of preterm delivery by conducting a meta-analysis of prospective cohort studies. Methods: PubMed, Embase, and Wangfang databases were searched through January 2012 to identify studies that met pre-stated inclusion criteria. Data were extracted using standardized forms. Either a fixed- or a random-effects model was used to calculate the overall combined relative ratio (RR) with its corresponding 95% confidence interval (95% CI) to evaluate the relationship between thyroid antibodies and preterm delivery risk. Subgroup analyses were mainly performed by type of thyroid antibodies including thyroid peroxidase antibody (TPO-Ab) and thyroglobulin antibody (TG-Ab). Results: Eleven prospective cohort studies involving 35 467 participants were included. The combined RR of preterm delivery for pregnant women with thyroid antibodies compared with the reference group was 1.41 (95% CI 1.08-1.84, P = 0.011). Subgroup analysis yielded the combined RR of preterm delivery for pregnant women with TPO-Ab compared with the reference group was 1.69 (95% CI 1.19-2.41, P = 0.003), whereas pregnant women with positive TG-Ab had no obvious risk of preterm delivery compared with the reference group (RR = 0.88, 95% CI 0.60-1.29, P = 0.513). Sensitivity analysis restricted to studies excluding women with thyroid dysfunction yielded similar results. Meta-regression analysis suggested that the status of exclusion or inclusion of women with thyroid dysfunction was the major source of heterogeneity in this meta-analysis. No evidence of publication bias was observed. Conclusions: Current evidence suggests that the presence of TPO-Ab in pregnant women significantly increases the risk of preterm delivery.