How can pregnancy cause a woman to make an antibody to a red blood cell antigen?

Question

Quizplus · Accepted Answer

During pregnancy, fetal red blood cells can cross the placenta and enter the mother's circulation. If the fetus inherits a red blood cell antigen from the father that is foreign to the mother, her immune system may recognize it as foreign and produce antibodies against it. This condition is known as hemolytic disease of the newborn or Rh disease. Antibodies produced by the mother can cross the placenta and destroy fetal red blood cells, leading to anemia and other complications. This can be prevented by administering Rh immunoglobulin to the mother during pregnancy and after delivery.

How Can Pregnancy Cause a Woman to Make an Antibody