Which type of immunity occurs when a fetus receives antibodies from the mother?

Naturally acquired passive immunity refers to the transfer of antibodies from mother to fetus, which occurs during pregnancy. This usually happens through the placenta, allowing the fetus to acquire maternal antibodies that provide immediate protection against infections during the early months of life. This type of immunity is considered "passive" because the fetus is not actively producing its own antibodies; rather, it is receiving them from another individual (the mother).

In contrast to passive immunity, active immunity involves the body actively generating its own immune response, typically through infection or vaccination. Therefore, since the fetus does not synthesize these antibodies but receives them directly from the maternal blood supply, the passive nature of this immunity is crucial.

Artificially acquired passive immunity, on the other hand, involves the introduction of antibodies through medical interventions, such as infusions or injections, rather than through natural transfer. Lastly, naturally acquired active immunity would involve the individual developing their own immune response after exposure to a pathogen, which is not the case for the fetus receiving maternal antibodies. This distinction ensures the accurate identification of immunity types in the given context.