Final answer:
An Rh-negative mother carrying an Rh-positive fetus can develop anti-Rh antibodies after her first pregnancy with an Rh-positive baby. During subsequent pregnancies, these antibodies can cross the placenta and cause hemolytic disease of the newborn, attacking and destroying the fetus's red blood cells and potentially leading to severe anemia or death without treatment.
Step-by-step explanation:
The harm to the fetus in the case of an Rh-negative mother carrying an Rh-positive fetus occurs through a process that starts with the mother's first exposure to Rh-positive blood. This can take place when she delivers her first Rh-positive baby and her immune system becomes sensitized to the Rh antigen present on the surface of the baby's red blood cells (RBCs). After this initial sensitization, the mother's immune system begins producing anti-Rh antibodies. If the mother becomes pregnant with a second Rh-positive baby, these antibodies can cross the placenta and attack the fetal RBCs, a condition known as hemolytic disease of the newborn (HDN) or erythroblastosis fetalis. This disease process can result in severe anemia, agglutination and hemolysis of the fetus's RBCs, and without medical intervention, it may be fatal to the fetus.
- Rh-negative mother delivers healthy first Rh-positive baby and is exposed to the Rh+ antigens.
- Rh-negative mother makes anti-Rh antibodies.
- Rh-negative mother is pregnant with second Rh-positive baby.
- Anti-Rh antibodies cross the placenta.
- Anti-Rh antibodies destroy Rh-positive baby's RBCs.