If a mother passes an antibody to her fetus through the placenta, what type of immunity does the fetus have?

• A. Naturally acquired passive immunity
• B. Artificially acquired passive immunity
• C. Naturally acquired active immunity
• D. Artificially acquired active immunity

Answer: (B)

The fetus gains immunity through passive transfer of maternal antibodies across the placenta, which is naturally acquired passive immunity. This means the fetus is protected by antibodies produced by the mother, not by its own immune response. It’s passive because the antibodies come from outside the fetus, and natural because this transfer occurs through normal physiology during pregnancy, not from vaccination or any medical intervention. The fetus isn’t producing antibodies itself, so the protection is immediate but temporary, waning as maternal antibodies decline and the infant’s own immune system takes over.