Final answer:
Isoimmunization (Rh incompatibility) occurs when an Rh-negative mother is pregnant with an Rh-positive fetus, leading to the production of antibodies that can attack the fetal red blood cells in subsequent pregnancies. It is preventable through administering Rho(D) immune globulin to the mother.
Step-by-step explanation:
Isoimmunization, also known as Rh incompatibility, is a condition that can occur when an Rh-negative mother is pregnant with an Rh-positive fetus. This mismatch can lead to the mother's immune system developing antibodies against the fetus's Rh-positive red blood cells. This condition does not usually pose a risk during the first pregnancy because the sensitization process—where the mother starts producing anti-Rh antibodies—typically begins after the fetal cells enter the maternal circulation, which often occurs during delivery. Consequently, there isn't enough time for the mother's immune system to affect the first Rh-positive baby significantly.
However, during subsequent pregnancies with Rh-positive fetuses, these preformed antibodies can cross the placenta, attack the fetal red blood cells, and cause hemolytic disease of the newborn (HDN). To prevent this, Rho(D) immune globulin (e.g., RhoGAM) injections are administered to the Rh-negative mother during pregnancy and after childbirth to neutralize any Rh-positive fetal cells that have entered the mother's bloodstream, preventing her immune system from being sensitized.
Therefore, the correct statement regarding isoimmunization (Rh incompatibility) is that it results from an Rh-negative mother carrying an Rh-positive fetus (b). Options a, c, and d are incorrect; isoimmunization can occur in subsequent pregnancies, poses risks to the newborn, and can be prevented, often through appropriate prenatal care involving the administration of Rho(D) immune globulin.