Rh Blood Group Incompatibility

Etiology of Rh Incompatibility

• A, B, O blood types are primary, but Rh (CDE) is another significant blood group
• Rh blood type is determined by the presence or absence of the D antigen
• Gene complexes can be CDE, cde, cDE, cDe, Cde, cdE, CDE, CdE

Incidence of Rh Negativity

• Rh negativity occurs in about 10% of the general population

Pathophysiology of Rh Incompatibility

• Fetus inherits Rh antigen from its father and the mother lacks the Rh antigen
• Rh+ Fetal RBCs enter maternal circulation, causing fetomaternal hemorrhage at delivery
• Fetal RBCs are destroyed by hemolysis, releasing bilirubin, which is cleared by the placenta
• This leads to a shift in oncotic pressure and anemia, causing RBC destruction

Maternal Immune Response

• Antibodies are formed in response to fetal Rh+ antigen
• Alloimmunization can occur in the 1st trimester
• Enough RBCs in maternal circulation can cause alloimmunization

Events that can Trigger Maternal Immune Response

• Childbirth
• Ectopic gestation
• Incomplete abortion
• Spontaneous abortion
• Voluntary termination
• Amniocentesis
• External cephalic version
• Direct abdominal trauma
• Placental delivery

Other Blood Groups

• Kell
• La