ABO incompatibility results when fetal blood type differs from maternal blood type.

The major blood typesareA, B and O. The major forms of incompatibility between the mother and fetus are : when the mother is O and the fetus is B or A or AB (most common); when the mother is A and the fetus is B or AB (uncommon); and when the mother is B and the fetus is A or AB (uncommon). In these cases the mother creates antibodies against the incompatible blood type. These antibodies cross the placenta into the infant's blood stream where they begin to destroy the same type blood cells. ABO incompatibility is similar to Rh incompatibility but generally creates much milder problems than Rh incompatibility. Neonates affected by ABO incompatibility may have elevated levels of bilirubin and become jaundiced. Severe incompatibility problems may require an exchange transfusion. However, most ABO incompatibility is relatively minor and the jaundice it produces can usually be treated with bili-lights (phototherapy).

Blood type form proteins or antibodies in people, they cause their immune system to react against other blood types. When their body is exposed to any other blood type the incompatibility or disorder occurs and causes the person to feel Back pain, get Blood in urine, Feeling of "impending doom", feeling Feverish and Yellow skin jaundice. During any kind of blood transfusion it is necessary to check the blood type to prevent any complication.

Prevention is not practical. Early recognition of an incompatibility allows for easy and inexpensive treatment.