Final answer:
Hemolytic disease of the newborn (HDN) occurs when an Rh- woman carries an Rh+ baby. During the first pregnancy, the baby is usually unaffected because the mother does not have enough time to mount a strong immune response. However, in subsequent pregnancies with an Rh+ fetus, the mother's secondary antibody response produces higher quantities of anti-Rh factor IgG, which can cross the placenta and cause HDN.
Step-by-step explanation:
Hemolytic disease of the newborn (HDN) occurs when an Rh- woman carries an Rh+ baby. This happens because if the mother is exposed to the Rh+ fetal red blood cells during pregnancy or delivery, her immune system will produce anti-Rh factor IgG antibodies. During the first pregnancy, the baby is usually unaffected because the mother does not have enough time to mount a strong immune response. However, in subsequent pregnancies with an Rh+ fetus, the mother's secondary antibody response produces higher quantities of anti-Rh factor IgG, which can cross the placenta and cause HDN.