• Destruction of fetal RBCs by maternal anti-Rh (D antigen) IgG antibodies that cross the placenta
  • Mechanism
    • 1st pregnancy
      • mother is Rh- and fetus is Rh+
      • mother is exposed to fetal blood at some point during pregnancy or delivery and generates anti-Rh IgG antibodies
    • 2nd pregnancy
      • mother is Rh- and fetus is Rh+
      • maternal anti-Rh IgGs cross the placenta and attach to fetal RBCs
      • fetal splenic macrophages phagocytose IgG coated RBCs
  • Symptoms
    • severe infant anemia shortly after birth
      • more severe than ABO HDN
      • symptoms worsen after birth because the maternal liver metabolizes fetal bilirubin
  • Serology
    • positive direct and indirect Coombs tests on cord blood
  • Exchange transfusions
Prognosis, Prevention, and Complications
  • Complications
    • Erythroblastosis fetalis  
    • kernicterus
  • Prevention of initial Rh exposure is critical 
    • Rh negative mothers receive anti-D globulin during 28th week of pregnancy
    • anti-D globulin hemolyzes fetal RBCs that enter maternal circulation before an immune reaction can be mounted against the Rh antigen
    • prevents formation of anti-Rh IgG in mother

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