Ans. is 'c' i.e., IgM antibody in fetal blood Laboratory diagnosis o Isolation of virus in cell cultures of throat samples, urine or other secretions. o Normally, maternal rubella antibodies in the form of IgG is transferred to infants and is gradually last over a period of 6 months. Persistent beyond 1 year in an unvaccinated child suggests the diagnosis of congenital rubella. o Presence of Ig M antibodies is diagnostic. o PCR for rubella RNA.