Ethnic Differences in Preterm Birth Risks for Pregnant Women with Thyroid Dysfunction or Autoimmunity: A Meta-analysis.

Objective: Abnormal maternal thyroid function is associated with preterm birth. However, this association stays dubious in relevant individual studies for ethnic difference reasons and lack of direct supporting data. This study aimed to evaluate the relationship between preterm birth and thyroid dysfunction or autoimmunity based on ethnic differences.

Methods: Relevant studies were identified through searches of MEDLINE, Excerpta Medica, Wan Fang, China Biological Medicine disc, and China National Knowledge Infrastructure from inception to June 15, 2016. Original articles in which an incidence or prevalence of thyroid dysfunction or autoimmunity before second trimester of pregnancy could be extracted were included.

Results: Thirty-two unique studies were included for the final meta-analysis. Patients involved were divided into two groups: Group 1 (G1) and Group 2 (G2) comprising of Asian and Caucasian populations, respectively. Positive thyroid antibodies were associated with the occurrence of preterm birth in both G1 [odds ratio (OR): 3.62, 95% confidence interval (CI): 2.83-4.65] and G2 (OR: 1.35, 95% CI: 1.17-1.56); hypothyroidism, only in G2 (OR: 1.20, CI: 1.09-1.33); and subclinical hypothyroidism or hypothyroxinemia, in neither group.

Conclusion: Thyroid autoimmunity may be a more favorable factor leading to preterm birth among pregnant women of different ethnicities, compared with thyroid dysfunction.