This test measures the levels of IgG antibodies against rubella, the virus responsible for causing German measles. If a woman contracts rubella early in pregnancy, it can lead to serious complications for the infant, including heart defects, growth retardation, hearing loss, blood disorders, vision problems, or pneumonia. If the mother is infected during pregnancy, the baby may also face long-term issues, such as central nervous system disorders, immune dysfunction, or thyroid problems.