Final answer:
Rh immunization occurs when Rh positive fetal blood crosses into maternal blood, stimulating maternal antibodies(option 2) against the fetal Rh antigen in an Rh-negative mother. This immune response can lead to hemolytic disease of the newborn in subsequent pregnancies if untreated.
Step-by-step explanation:
Rh immunization in a pregnant client develops under specific conditions when there is Rh factor incompatibility between the mother and the fetus. The correct condition for the development of Rh immunization is when Rh positive fetal blood crosses into maternal blood, stimulating maternal antibodies. This happens when an Rh-negative mother carries an Rh-positive fetus. During the birth of the first Rh-positive child, some of the fetal blood cells can enter the maternal bloodstream. If these cells are Rh-positive, and the mother is Rh-negative, her immune system may produce anti-Rh antibodies. This primary immune response is called sensitization. In a subsequent pregnancy with another Rh-positive child, these anti-Rh antibodies can cross the placenta and potentially cause hemolytic disease of the newborn (HDN), also known as erythroblastosis fetalis, which can result in severe anemia or even fetal death if untreated.
To prevent this condition, Rh-negative mothers are given Rho(D) immune globulin during and after pregnancy, which targets any Rh-positive fetal blood cells in the mother's bloodstream to prevent immunization. Hence, the correct option for the given question is 2. Rh positive fetal blood crosses into maternal blood, stimulating maternal antibodies.