OPTION 1

EXPLANATION:

• Phylogenetically, IgM is the oldest immunoglobulin class. It is also the earliest immunoglobulin to be synthesised by the fetus, beginning by about 20 weeks of age.
• As it is not transported across 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 syphilis, rubella, HIV infection and toxoplasmosis.
• IgM antibodies are relatively short-lived, disappearing earlier than IgG. Hence, their demonstration in serum indicates recent infection. Deficiency of IgM antibodies is associated with septicemia.