Which class of antibody crosses the blood-placenta barrier and protects newborns for the first months of life until they produce their own antibodies?

The class of antibody that crosses the blood-placenta barrier to provide essential protection to newborns is IgG. This antibody is unique among immunoglobulins in that it is the only type that can traverse the placenta during pregnancy. As a result, maternal IgG antibodies are transferred to the fetus and provide passive immunity. This passive immunity is crucial for newborns in the early months of life, as they have not yet developed their own immune response and are vulnerable to infections.

IgG antibodies help protect the infant against various pathogens until their immune system begins to mature and produce its own specific antibodies, which typically starts to occur over the first few months after birth. The presence of maternal IgG gives infants a vital defense during this period when their immune systems are still developing, helping to reduce the risk of serious infections.

Other immunoglobulins, such as IgD, IgA, and IgM, do not have the same capability of crossing the placenta as IgG does. Each of these antibodies plays distinct roles in the immune system but does not provide the same level of passive protection to the fetus or newborn.