How can Rh incompatibility cause hemolytic disease of the newborn?

Rh incompatibility causes erythroblastosis fetalis—also known as hemolytic disease of the newborn—when an Rh-negative mother carries an Rh-positive fetus.123

The process typically occurs as follows:

• Sensitization: During the birth of an Rh-positive child, fetal red blood cells carrying the Rh factor may enter the mother's bloodstream. This exposure sensitizes the mother’s immune system, causing her to produce anti-Rh antibodies.1432
• Hemolysis: In subsequent pregnancies with an Rh-positive fetus, these maternal antibodies can cross the placenta and enter the fetal circulation. Once there, they attack and destroy the fetus's red blood cells, a process called hemolysis.1352

This destruction of red blood cells leads to anemia, jaundice, and potentially severe complications like heart failure or brain damage. Today, this condition is largely preventable by administering Rh immunoglobulin to the mother, which destroys fetal cells in her circulation before her immune system can become sensitized.1543