Which immunoglobulin is provided to a newborn by the mother?

• A. IgG
• B. IgD
• C. IgM
• D. IgA

Answer: (A)

Maternal antibodies reach the newborn primarily to supply systemic protection through the placenta. Immunoglobulin G is the only class transferred in significant amounts across the placenta, via specific receptors, giving the infant passive systemic immunity at birth. In contrast, IgM is too large to cross the placental barrier, so it does not provide fetal systemic immunity. IgA appears in breast milk and helps protect the newborn’s mucosal surfaces after birth, but it does not establish systemic immunity. IgD mainly serves as a B-cell receptor and isn’t a meaningful source of maternal antibodies for the newborn. So the immunoglobulin provided to a newborn by the mother is IgG.