A mother with no prenatal care gives birth to a term infant with findings of IUGR, microcephaly, hepatosplenomegaly, thrombocytopenia, and during later testing sensorineural hearing loss. You are concerned about cytomegalovirus (CMV). The most important diagnostic study for CMV evaluation for a newborn is: a. Viral culture b. Brain biopsy c. Viral PCR d. Rapid plasma reagin (RPR) e. Antibody titers