Which immunoglobulin crosses the placenta to provide neonatal protection?

The immunoglobulin responsible for crossing the placenta and providing essential protection to the neonate is IgG. This particular antibody is critical for the immune defense of the fetus during pregnancy and continues to be present in the newborn for several months after birth.

IgG is the only immunoglobulin that can transfer from the maternal circulation to the fetus through the placenta, making it vital for passive immunity. This transfer allows the newborn to acquire antibodies against pathogens the mother has been exposed to, thereby helping to protect the infant during their initial months of life when their own immune system is still developing.

In contrast, IgA primarily provides protection on mucosal surfaces and is found in breast milk, while IgM is involved in the early response to infections but does not cross the placenta. IgE is associated with allergic reactions and parasitic infections and also does not cross the placental barrier. The role of IgG in providing this transplacental immunity is crucial for the health of neonates, especially those born prematurely or with reduced immune function.