Pregnancy, Birth and Beyond

ABO Incompatibility in Newborns

ABO incompatibility is a common and generally mild type of haemolytic disease in babies. The term haemolytic disease means that red blood cells are broken down more quickly than usual.


Red blood cells

ABO incompatibility is a common and generally mild type of haemolytic disease in babies. The term haemolytic disease means that red blood cells are broken down more quickly than usual which can cause jaundice, anaemia and in very severe cases can cause death. During pregnancy, this breakdown of red blood cells in the baby may occur if the mother and baby’s blood types are incompatible and if these different blood types come into direct contact with each other and antibodies are formed.

Significant problems with ABO incompatibility occur mostly with babies whose mothers have O blood type and where the baby is either A or B blood type. Premature babies are much more likely to experience severe problems from ABO incompatibility, while healthy full term babies are generally only mildly effected.  Unlike haemolytic disease that can result in subsequent babies when a mother has a negative blood group, ABO incompatibility can occur in first-born babies and does not become more severe in further pregnancies.

To help you understand ABO incompatibility, it is helpful to review the different blood groups. The genes you inherit from your parents determine your blood group. There are four blood types; A, B, AB and O. Each blood type has its own individual collection of chemicals on the blood cell surface known as antigens, so type A has the A antigen, B has the B antigen, AB has both antigens and O contains no antigen. If different blood types mix, an immune response occurs and the person will produce antibodies to attack the foreign blood antigen.

Jaundice newborn baby
 Jaundice Baby

During pregnancy the mother’s and baby’s blood generally do not mix. The mothers and babies circulation is kept separate by the placental membrane.  Oxygen, carbon dioxide, nutrients, certain drugs and some viruses can pass through the placental membrane. However, some circumstances can cause the two blood types to mix, such as miscarriage, trauma and birth, and sometimes they may mix for reasons unknown. Antibodies against the foreign blood types A and B may be formed. These antibodies could then pass across the placental membrane into the baby’s circulation and may result in the destruction of some of the baby’s red blood cells. This destruction of red cells causes an increase in the production of bilirubin – a waste product. If too much bilirubin is produced, it can overwhelm the baby’s normal waste elimination processes and lead to jaundice.

Jaundice is caused by bilirubin, a yellow pigment that gives the newborn's skin and whites of the eyes a yellow appearance. The baby’s colour is observed during regular newborn examinations by a midwife or doctor. The baby may need blood tests to check the level of bilirubin if the baby looks significantly jaundiced. Slight jaundice is very common in newborns and requires no follow up. Babies with high levels of bilirubin in their blood will require phototherapy and in severe cases they may need an exchange blood transfusion.

Jaudice baby under phototherapy lights
 Baby having phototherapy

For babies effected by ABO incompatibility, anaemia may become an issue after a few weeks. The anaemia is caused by the faster than normal breakdown of the baby’s red blood cells caused by the mother’s antibodies. These antibodies can linger in the baby’s circulation for weeks after birth. Because of this, some babies will need to have blood tests to check the level of anaemia.

Routine blood screening tests in pregnancy do not screen for ABO incompatibility. Testing in pregnancy is not recommended as antibody levels do not correlate well to actual ABO haemolytic disease in the baby. There are no preventative measures that can be taken.

After birth there are two options for testing for ABO incompatibility: