BACKGROUND Primary human cytomegalovirus (CMV) infection during pregnancy is a major cause of congenital malformation. We detected primary CMV infection in pregnant Korean women by using an algorithm that comprises CMV IgG, IgM, and IgG avidity tests. METHODS During a 2-month period, 744 pregnant women who were at 10-19 weeks of gestation were consecutively enrolled in this study. Human anti-CMV IgG and IgM levels in their sera were determined by chemiluminescence immunoassays. Serum samples from the women who were positive for CMV IgG and IgM were assayed by the ARCHITECT CMV IgG avidity test in order to distinguish primary from non-primary CMV infection. Gross examination of the neonates of the women who were positive for CMV IgM was conducted. RESULTS The seroprevalence of CMV IgG and IgM was estimated to be 98.1% and 1.7%, respectively. The samples from all the women who were positive for CMV IgM or with grey zone results contained high avidity CMV IgG. Seven women with positive CMV IgG and IgM results who completed follow-up up to delivery showed no gross evidence of in utero CMV transmission. CONCLUSIONS Maternal primary CMV infection was not detected in any of the pregnant women included in this study cohort. CMV IgG avidity test enabled the identification of women who were at a low risk of transmitting CMV infection and provided informative for subsequent pregnancy outcomes. Compared to previous studies, the seroprevalence of CMV IgG antibody across pregnant Korean women remained unchanged.