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. Due to the increase break down of red blood cells, jaundice, anaemia, and in very severe cases can cause death, can result. During pregnancy ABO incompatibility may occur if:
* The mother and baby’s blood types are incompatible
* Different blood types come into direct contact with each other and,
* Antibodies form
Significant problems with ABO incompatibility occur mostly with babies whose mothers have the O blood type and where the baby is either A or B blood type. Premature babies are much more likely to experience significant problems from ABO incompatibility. Conversely, healthy full-term babies are generally only mildly affected. Unlike haemolytic disease that can result in the birth of a second baby when a mother has a negative blood group, ABO incompatibility can occur in first-born babies. Additionally, it does not become more severe in future pregnancies.
Understanding ABO Incompatibility
When understanding 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 collection of chemicals on the blood cell surface known as antigens. To clarify, type A has the A antigen, B has the B antigen, AB has both antigens and O contains no antigen. Therefore if different blood types mix, an immune response occurs. As a result, the person may produce antibodies to attack the foreign blood antigen.
During pregnancy, the mother’s and baby’s blood generally do not mix. It’s important to realise that the mothers and babies circulation is kept separate by the placental membrane. Though oxygen, carbon dioxide, nutrients, certain drugs and some viruses can pass through the placental membrane. Furthermore, some circumstances may cause the two blood types to mix. Examples of events increasing the risk of the two blood types mixing include miscarriage, trauma and a babies birth. Surprisingly two blood types may mix for reasons unknown.
Antibodies form against foreign blood types such as type A and B. These antibodies could then pass across the placental membrane and enter the baby’s circulation. Antibodies can destroy 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 the baby’s body produces too much bilirubin, it can overwhelm the baby’s normal waste elimination processes and lead to jaundice.
An increase in bilirubin causes jaundice, a pigment that turns the newborn’s skin yellow. Additionally, jaundice can cause the whites of the baby’s eyes to have a yellow appearance. During an examination, your midwife or doctors observers the colour of your baby’s skin. If your baby looks yellow, performing a blood test can confirm the level of jaundice. Slight jaundice is very common in newborns and requires no follow-up. Babies with high levels of bilirubin in their blood will require phototherapy. Furthermore, severe cases of jaundice may need an exchange blood transfusion.
Anaemia in Babies
For babies effected by ABO incompatibility, anaemia may become an issue after a few weeks. The anaemia is caused by the faster than usual 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 Testing
Routine blood screening tests in pregnancy doesn’t screen for ABO incompatibility. Furthermore, testing in pregnancy does not improve outcomes for the baby. Unfortunately, there are no preventative measures for ABO incompatibility.
After birth, there are two options for testing for ABO incompatibility:
- Have the cord blood of all babies whose mothers have an O blood group and the father either type A or B blood tested. The theory behind this approach is that if the baby is either type A or B, and, they test positive for direct antiglobulin tests (DAT), the baby can then be followed closely for jaundice.
- The alternate approach is to screen any baby who becomes significantly jaundiced (particularly within the first 24 hours).