Rubella, also known as German measles, is generally mild for most people, causing a slight fever and rash that disappear in a few days. Most children are vaccinated against it with the MMR (measles-mumps-rubella) or MMRV (which also includes chickenpox) vaccines. However, rubella can be very serious for pregnant women, especially in the first four months, potentially causing severe birth defects. A blood test can determine if you have rubella antibodies. Antibodies are proteins made by your immune system to fight infections. There are two types of antibodies for rubella: IgM and IgG. IgM appears first after infection and stays for 7-10 days in adults and up to a year in newborns. A positive IgM test indicates a recent infection, but it can sometimes be a false positive. IgG stays in the bloodstream for life, indicating past infection or vaccination and immunity. Pregnant women and newborns may need both tests. A positive IgM in a newborn means they were infected before or just after birth. A negative IgM usually means no infection, but people with weak immune systems might not produce enough antibodies to show up in the test. IgG results can vary; a low score might mean recent vaccination, and retesting could be necessary.