Question

Which of the following immunoglobulins primarily pass through the placenta to provide passive immunity to the fetus?

• A. IgM only
• B. IgM and IgG
• C. IgA and IgG
• D. IgG only

Hint:

IgG is the only immunoglobulin that crosses the placenta, providing the fetus with passive immunity, especially in the third trimester.

Answer 1

The Correct Option is D

Step 1: Understand the role of immunoglobulins.
Immunoglobulins (antibodies) are essential components of the immune system. During pregnancy, maternal antibodies provide passive immunity to the fetus. This protection is critical before the fetus's own immune system becomes fully functional.

Step 2: Evaluate the immunoglobulins:

• IgM: First antibody produced in response to infection, does not cross the placenta due to its large pentameric structure.
• IgG: The only immunoglobulin that crosses the placenta. It provides systemic passive immunity to the fetus.
• IgA: Found mainly in mucosal secretions (e.g., saliva, breast milk), does not cross the placenta.
• IgM and IgG (Option 2): Incorrect. Only IgG can cross the placenta.

Step 3: Conclusion.
The correct immunoglobulin that crosses the placenta and provides passive immunity to the fetus is IgG only.

Correct Answer: Option (4)