Which antibody is known to cross the placenta?

Which antibody is known to cross the placenta?

• A. IgA
• B. IgD
• C. IgM
• D. IgG

Answer: (D)

The antibody that is known to cross the placenta is IgG. This is crucial for providing passive immunity to the fetus during pregnancy. IgG is the most prevalent antibody in the blood and extracellular fluid, making up around 75-80% of the total immunoglobulin pool in a healthy adult. Its structure allows it to traverse the placental barrier, thereby enabling the transfer of maternal antibodies to the developing fetus. This transfer helps to protect the newborn during the early stages of life when their own immune system is still maturing.

In contrast, other antibodies such as IgA, IgD, and IgM do not have the same capability to cross the placenta. IgA is primarily found in mucosal areas and provides immune protection in secretions like saliva and breast milk but does not cross the placental barrier. IgD plays a role mainly in the activation of B cells and is present in very small amounts in serum, making it not relevant for placental transfer. IgM, the first antibody produced in response to infection, is a larger molecule that generally cannot cross the placenta due to its size and structure.

The unique ability of IgG to pass through the placenta underscores its significant role in fetal immunity and highlights the importance of maternal health during