Abstract： Objective:To investigate the role of methylation of placental glucocorticoid response gene in the association between pregnancy-related anxiety in the third trimester and birth outcomes.Methods:Based on a prospective cohort study, singleton live births and their mothers from the Ma′anshan Birth Cohort Study (MABC) were included as participants in this study. The maternal pregnancy-related anxiety symptoms in the third trimester of pregnancy were evaluated by using the Pregnancy-related Anxiety Questionnaire. The neonatal birth outcomes were collected from medical records. The placental tissues from 300 pregnant women with pregnancy-related anxiety and 300 without pregnancy-related anxiety were collected to detect the methylation of FKBP5, NR3C1 and HSD11B2 genes using the Methyl Target approach. The methylation factors were extracted by exploratory factor analysis. Linear regression or logistic regression models were used to analyze the association between pregnancy-related anxiety in the third trimester, methylation factor scores, and birth outcomes. The mediating role of methylation factors in the association between pregnancy-related anxiety in the third trimester and birth outcomes was analyzed by using the Process procedure. Results:The mean age of 2 833 pregnant women was (26.60±3.60) years old. After adjusting for confounding factors, pregnancy-related anxiety in the third trimester increased the risk of small-for-gestational-age ( OR=1.32, 95% CI:1.00-1.74). A total of 5 methylation factors were extracted, and the factor 5 was loaded with FKBP5 CpGs 18-21. Pregnancy-related anxiety in the third trimester was negatively correlated with the factor 5 ( β=-0.24,95% CI:-0.44--0.05). The factor 5 was positively correlated with the gestational age ( β=0.17, 95% CI:0.06-0.27). In addition, the factor 2 ( β=0.02,95% CI:0.00-0.04) and factor 3 ( β=0.03,95% CI:0.01-0.05) were positively correlated with 5-min Apgar score after delivery. However, this study did not found the mediating role of the scores of the factor characterized by FKBP5 in the relationship between pregnancy-related anxiety and birth outcomes. Conclusion:Pregnancy-related anxiety in the third trimester may reduce the methylation level of FKBP5 CpGs 18-21 in placental tissues and is associated with the risk of small-for-gestational-age.