Immunoglobulin secreted by fetus as primary response

Ans. is 'b' i.e., IgM IgM is the first immunoglobulin class produced in a primary response to an antigen. IgM antibodies are relatively sho lived, disappearing earlier than IgG. IgM is the earliest immunoglobulin to be synthesized by the fetus beginning by about 20 weeks of age. IgM can not cross the placenta. The presence of IgM in the fetus or newborn indicates intrauterine infection and its detection is useful in the diagnosis of congenital infections such as Toxoplasmosis, syphilis, rubella, cytomegalovirus infection and HIV infection.