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What is it:

Blood antigen incompatibility is when the fetal blood type/Rh factor (that of the baby) differs from that of the mother's blood type/Rh factor (maternal)

Kinds of Incompatibility:

  1. Rh factor (Rhesus factor): this occurs when a Rh negative mother has a infant that is Rh positive. 

  2. ABO:  this occures when the fetal blood type differs from the maternal blood type.


Rh factor is determind by running a lab test in which artifically antibodies


A, B and O are the three major blood types.  ABO incompatibility between the mother and Fetus can occur if:

  • the mother is O and the fetus is B, A, or AB.  (Most common-represents almost 100 percent of the cases)

  • the mother is A and the fetus is B or AB (extremely uncommon)

  • the mother is B and the fetus is A or AB (extremely uncommon)

In these cases, the mother creates antibodies against the fetus' incompatible blood type.  These antibodies cross the placenta into the fetus' blood stream where they begin to destory the fetus' blood cells.

ABO incompatibility is similar to Rh incompatibility but generally creats much milder problems the Rh imcompatiblity.  Newborn infants affected by ABO incompatibility may have elevated levels of bilirubin and come jaundiced (whites of the eyes and skin become yellow).  Severe ABO incompatibility problems may require and exchange transfusion.  However, most ABO incompatibility is relatively minor and the jaundice it produces can usually be treated with bili-lights (phototherapy).