Maad Rayan Publishing Company Biomedical Research Bulletin 2980-9924 3 2 2025 06 30 Clinical Relevance of IgG Avidity Testing for Identifying Acute Rubella Infection in Women of Reproductive Age 61 65 10.34172/biomedrb.9066 EN Farideh Elahimanesh https://orcid.org/0000-0001-8744-8251 Sajad Borzoueisileh https://orcid.org/0000-0003-4148-135X Nayer Seyfizadeh https://orcid.org/0000-0001-9744-7252 Shahnaz Sabetkam Davoud Hassanzadeh Journal Article 10.34172/biomedrb.9066 2025 06 15 2025 06 21 Background: Rubella virus infections during pregnancy are known to have considerable teratogenic effects. Maternal infection can lead to congenital rubella syndrome (CRS), a condition with lifelong complications. In fact, individuals affected by CRS often show higher rates of diabetes, osteoporosis, and thyroid dysfunctions in later life. This study aims to highlight the importance of distinguishing recent from past rubella infections in the earliest stages of pregnancy. Methods: A total of 212 pregnant women were included in the study. They were in the second to fourth months of gestation and were considered at risk of rubella virus infection. At the beginning of pregnancy, serum samples were collected, and anti-rubella IgG and IgM levels were measured using a standard ELISA kit. IgG avidity was assessed using the method proposed by Hedman et al, following the avidity index (AI) protocol with the Euroimmun diagnostic kit. Results: Among the 162 serum samples analyzed during the first trimester, participants were categorized into 3 distinct groups based on their serological profile. Group A consisted of 100 individuals (61.7%) who tested positive for both IgG and IgM. Group B included 8 individuals (4.9%) who were IgG positive but IgM negative. Group C comprised 54 individuals (33.3%) who tested negative for IgG but positive for IgM. This categorization offered a clearer understanding of immune status and potential recent infection. Conclusion: The findings of this study highlight the practical value of IgG avidity testing in early pregnancy. By enabling clinicians to more accurately differentiate between acute and past infections, the test plays a critical role in supporting timely medical decisions, potentially helping to prevent complications associated with rubella in unborn children.