Objective To evaluate the relationship between positive thyroid autoantibody and risk of preterm birth.Methods Literature search was done in PubMed,Embase,China Academic Journal Network Publishing Database,Wanfang Medical Database and China Biology Medicine disc databases from January 1st,1989 to January 26th,2012.Criteria for inclusion included:(1) Prospective cohort study; (2) The exposure was positive thyroid autoantibody and outcome was preterm birth; (3) The enrolled subjects were pregnant women without cardiovascular or rheumatic disease; (4) Relative risk (RR) and its 95％ confidence interval (95％CI) of preterm birth were provided in the study.Meta-analysis was performed by Stata 12.0.The relationship between positive thyroid autoantibody and risk of preterm birth was evaluated by RR and 95％ CI.Results Ten cohort studies were enrolled.One thousand six hundred and fifty seven cases of preterm birth occurred among 25 081 pregnant women.Heterogeneity among the 10 studies was found in meta-analysis (I2 =79.2％,P＜0.01).The risk of preterm birth in pregnant women with positive thyroid autoantibody was higher than those in control group by random effects analysis (RR=1.61,95％CI:1.18-2.20,P＜0.05).Subgroup analysis was further performed.In five studies,the cases of control group were pregnant women with normal thyroid function; heterogeneity was not found in these five studies (I2=39.1％,P=0.160); and RR of the risk of preterm birth was 2.55 in pregnant women with positive thyroid autoantibody (95 ％ CI:2.04 3.19,P＜0.01).In the other five studies,the cases of controlgroup were pregnant women who had not been ruled out the possibility of thyroid dysfunction;heterogeneity was not found in these five studies either (I2 =0.0％,P =0.970); and RR was 1.18(95 ％ CI:1.01-1.37,P＜0.05).After excluding two low-quality studies,RR of the risk of preterm birth was 1.72 in pregnant women with positive thyroid autoantibody (95％CI:1.18 2.53,P＜0.05).The funnel plots presented symmetrical graphics,indicating that there was no publication bias.Conclusions Positive thyroid autoantibody in pregnant women is a risk factor of preterm birth.