ABO Compactibility

If blood group O woman have a baby, the mom will have a problem with ABO incompatibility b/c mom already have an Ab that can cross the placenta (blood group O people have anti A IgM, anti B IgM and anti AB IgG, normally).  Normally, there is an anti AB IgG Ab which can cross the placenta, and attack an A or B RBC. So, there could be a problem in the very first pregnancy. 

 EXAMPLE

A mom wtih blood group O negative and baby is blood group A-negative.  Is there an incompatibility of blood groups? Yes. Is there an incompatibility in Rh groups? No.  Just the blood groups, since the mom is O while baby is A.  The mom is O, she has anti AB IgG, which will cross the placenta; the A part of the Ab will attach to the A part of the A cells of the baby’s.  The baby’s macrophages of the spleen will destroy it, which is Type II HPY, mild anemia, and unconjugated bilirubin which is handled by the mom’s liver; no kernicterus, no probs with jaundice in the baby b/c in utero, the mom’s liver will take care of it.  When the baby is born the baby, it will have a mild anemia and jaundice.  MCC jaundice in the first 24 hrs for a newborn = ABO incompatibility (not physiologic jaundice of the newborn – that starts on day 3).   

Why did the baby develop jaundice? B/c the baby’s liver cannot conjugate bilirubin yet and must handle unconjugated bilirubin on its own now, so it builds up. This is an exchange transfusion reaction for ABO incompatibility – most of the time is b9, and put under UV B light.   

How does UV B light work? 

It converts the bilirubin in the skin into di-pyrol, which is water soluble and they pee it out (Rx for jaundice in newborn).  Anemia is mild b/c it is not a strong Ag and doesn’t holster a brisk hemolytic anemia.  If you do a coomb’s test, it will be positive b/c IgG’s on the RBC’s.  So always an O mom with a blood group A or AB baby.  This can occur from the first pregnancy (not like Rh sensitization where the first pregnancy is not a problem).  In any pregnancy, if mom is blood group O, and she has a baby with blood group A or B, there will be a problem (blood group O = no problem).