Case study: Hemolytic disease of the newborn

Transplacental transfer of IgG via FcRn can transport Abs from mother to fetus.

If a mother is Rh- and a baby is Rh+, the mother may become sensitized to the Rh factor present in the fetus and produce alloantibodies directed against the Rh factor.

Anti-Rh Abs cross the placenta and enter fetal circulation. These Abs bind to fetal RBCs, marking them for destruction.

Risk of sensitization is increased with subsequent pregnancies.

ABO incompatibility
Risk of sensitization is decreased if fetus is incompatible with mother.

Coombs test
Direct test = sample of fetus RBCs

Indirect test = sample of woman's serum incubated with Rh+ RBCs

Prevention
Passive immunization with low concentration of anti-Rh antibodies. The antibodies bind Rh+ fetal RBCs and FcγRIIBI, inducing apoptosis in the naive anti-Rh B cell.