This test can help determine Rubella-specific IgG avidity in human plasma or serum to differentiate between acute and past infection. The presence of Rubella Virus IgG antibodies indicates the occurrence of Rubella infection. However, it does not differentiate between recent and past Rubella infections. Rubella is also called German measles. It can cause a mild fever and rash that subsides within a few days. For pregnant women, Rubella can be very serious. If infected in the first four months, the baby can have hearing, eye, heart problems or have an early birth.