Hemolytic disease of the newborn

Principles to understand

• mother receives some fetal cells during delivery (around 2 mL, sometimes a bit more)

• some fetal cells leak across the placenta, usually in the last trimester

• this means that every Rh- mother with an Rh+ father has a potential for being immunized

• RhD is the most immunogenic of all Rh isotypes in Rh- mothers

  • you can get this disease against other Rh antigens, not just RhD, but you just usually don’t

• maternal IgG molecules cross placenta and causes hemolysis in Rh+ fetus

• Rhogam is given after birth of Rh+ babies to Rh- mothers to destroy fetal RBC and prevent immunization. if you give this fast enough, mother will not make antibodies because fetal RBC will not have been processed as antigen

  • say father is B+, mother is A-, and fetus is B+. then, the anti-B antibodies from mother will destroy fetus’s blood cells because the ABO mismatch is so immunogenic that it would lead to lysis of fetal blood cells. this would mean that the baby’s Rh+ red cells are destroyed, so this actually helps with the Rh antigen mismatch

• when attempting intrauterine transfusion, crossmatch blood to be compatible with the mother

Landsteiner’s blood types

• you should be able to deduce the reaction when mixing RBC types and serum types together

Maternal serum has antibodies

• maternal serum will agglutinate baby’s cells

• maternal serum will also agglutinate Rh+ O cells after her own cells have been spun out

• for high sensitivity of this test, rapid anti-human antibody facilitates agglutination—this is the Coombs test

What natural immune defense went wrong in this disease?

• it’s good to coat bacteria with antibodies and eat them

• this goes wrong when red cells are coated and they are eaten

Category: Pathology Notes