What is ABO incompatibility?

ABO incompatibility results when the fetal blood type is different from the mother’s blood type. When the blood types differ, the mother creates antibodies against the fetus’ incompatible blood type. These antibodies enter the placenta and begin to destroy the fetus’ blood cells.

What are the symptoms?

Incompatible maternal and fetal blood type as determined by prenatal testing, jaundice in the newborn, and elevated bilirubin level in the newborn.

What causes ABO incompatibility?

ABO incompatibility can occur between the mother and fetus under three scenarios. The blood types are: A, B, and O. The most common incompatibility occurs when the mother has O type blood and the fetus has B, A, or AB. The other combinations that cause ABO incompatibility are: the mother has A type blood and the fetus has A or AB type blood, or the mother has B type blood and the fetus has A or AB type blood. Both these last combinations are highly unlikely to occur.

How is ABO incompatibility diagnosed?

ABO incompatibility is diagnosed by: (1) cord blood test for incompatibility, (2) a complete blood count (CBC) that shows damaged and hemolyzed blood cells, and (3) elevated bilirubin levels.

How is ABO incompatibility treated?

ABO incompatibility is treated in newborns by light therapy (phototherapy). On rare occasions an exchange transfusion may be necessary. Full recovery usually occurs with no lasting repercussions.

Special considerations:

Complications can result from ABO incompatibility, such as anemia and kernicterus. Both conditions are rare.

Thomas G. Stovall, M.D.
Dr. Stovall is a Clinical Professor of Obstetrics and Gynecology at the University of Tennessee Health Science Center in Memphis, Tennessee and Partner of Women’s Health Specialists, Inc.