Background: Congenital infections are among the most important conditions threatening human fetal health, the majority of which are caused by viral agents. Screening pregnant women for viral infections is essential because such infections can cause serious consequences for both the mother and the infant. So, this study aimed to serologically investigate sexually transmitted viral infections in pregnant women and also find the association between the prevalence of viral infections and epidemiological parameters in pregnant women of Sari, Iran. Materials and Methods: This descriptive, observational study was performed in pregnant women referring to Sari Birth Cohort Center between 2018 and 2020. A total of 1092 blood samples were investigated for hepatitis B (HBV), hepatitis C (HCV), human immunodeficiency virus (HIV), human T-lymphotropic virus (HTLV), and cytomegalovirus (CMV) serological markers by enzyme-linked immunosorbent assay (ELISA). Results: The prevalence of HBsAg positivity, HCV, HIV, and HTLV was 0.2%, 0.09%, 0.09%, and 0.2%, respectively. The percentage of participants with CMV-IgM and -IgG antibody titers above normal was 0.2% and 91.8%, respectively. Pregnant women whose educational level was bachelor's degree or lower, those who did not use a male condom before pregnancy, or those with a family history of infectious disease were found to be more likely to have HBV, HCV, HIV, HTLV, and CMV infections. Conclusion: Family history, maternal age, pregnancy stage, and not using a male condom are among the risk factors for sexually transmitted viral infections in pregnant women in Sari.