ABO Incompatibility


ABO incompatibility is a complication that could possibly occur during pregnancy. It is an immune system reaction that takes place when an infant’s blood type is different from their mother’s type. As a result, the baby will be affected by the antibodies being produced by the mother.

abo blood system

Blood types are not the same from each other due to the small molecules found on the surface of the blood cells. Each individual owns a combination of these two molecules. Type O lacks any of the surface molecules. The different kinds of blood type are:

  • Type A – contains AA or AO molecules
  • Type B – contains BB or BO molecules
  • Type AB – contains one A and one B molecule
  • Type O – does not have any of the molecules

antigen a and antigen b

When blood types are mixed with each other, its immune system is automatically activated and antigens are produced. These antigens are the ones that create problems for the infant.

Checking for any compatibility of the blood is one of the main reasons why blood typing has been very significant in early pregnancy. Likewise, blood typing and matching before any blood transfusions or organ donation reduces the risk of acquiring any disease or blood incompatibility. The reaction triggered by an incompatible blood is similar to that of an allergic response.

Symptoms of ABO Incompatibility

Symptoms of ABO Incompatibility may include the following:

  • Fever
  • Back pain
  • Certain feeling of “impending doom”
  • Jaundice or yellow skin
  • Blood in the urine


During the period of pregnancy, the mixing of fetal and maternal blood rarely occurs since the circulation of blood from both the fetus and mother are partitioned by the placental barrier, preventing the combination of blood. Nonetheless, other things such as drugs, carbon dioxide, nutrients, oxygen, or any particular viruses could pass through the placental membrane.

The antibodies produced by a pregnancy woman are transported through the placenta, directly into the fetal circulation. This will then supply the newborn, whose immune system is still immature, with invaluable maternal antibodies in which the chance of fetal survival is boosted. The negative aspect of this survival process is when blood accomplishes to cross the placental barrier and allows the maternal antibodies to attack fetal red blood cells that may result to ABO Incompatibility.

In some instances, two blood types are allowed to mix. If maternal-fetal blood does manage to combine in a mother with one blood type and is pregnant with an infant who has a different blood type, antibodies opposed to the foreign blood are produced.

Unfortunately; these antibodies frequently pass via the placental barrier before getting to the fetal circulation, wherein they could damage and destroy a number of the growing cells of the fetus.

The damaged fetal red blood cells caused by the antibodies can result to an increase of bilirubin, as a waste product of red blood cells that is normally created by the liver in the fetal circulation of blood. An excessive amount of bilirubin may easily affect the neonate’s liver and lead to a condition known as neonatal jaundice.


ABO Incompatibility may be diagnosed by the physician through the following:

  • Physical examination
  • Bilirubin tests – It is a type of blood test that can assess the levels of bilirubin in the blood.
  • Urine tests – This test will show any hemoglobin caused by the breakdown of red blood cells.
  • Complete blood count (CBC) tests – It is a type of blood test that can check the overall health of a patient and detect certain disorders. Red blood cells can also be measured through this test. In ABO Incompatibility, the result will show damage to red blood cells or anemia.

The blood type of a donor is also evaluated through a blood test to see if it is compatible with the patient’s type.


Treatment options may include:

  • Phototherapy – Helpful for treating any newborn with jaundice
  • Steroids – To reduce allergies and swelling
  • Antihistamines – Used for treating any allergic reactions
  • Intravenous (IV) fluids – To manage the amount of fluids in the body
  • Exchange Transfusions – Recommended for severe cases wherein fetal blood is replaced by donated blood

abo incompatibility blood transfusions


Possible complications of ABO Incompatibility may include:

  • Low blood pressure
  • Kidney failure
  • Death
  • Anemia





Flegel WA (2011 Feb). Molecular genetics and clinical applications for RH. Transfus Apher Sci. 44(1):81-91.

Murray NA, Roberts IA (2007 Mar). Haemolytic disease of the newborn. Arch Dis Child Fetal Neonatal Ed. 92(2):F83-8.

Luchtman-Jones L, Schwartz AL, Wilson DB . The blood and hematopoietic system. Fanaroff AA, Martin RJ, eds. Neonatal-Perinatal Medicine-Diseases of the Fetus and Infant. 8th ed. St. Louis, Mo: Mosby Vol 2: 1287-1356.

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