What Is ABO Incompatibility?
ABO Incompatibility is a fairly common and milder type of hemolytic disease of newborns and is caused by the result of an immune system reaction. Rh Incompatibility, another hemolytic disease of the newborn, is associated with poorer fetal outcomes. ABO incompatibility occurs when blood from two different – and incomparable – types of blood are mixed together.
ABO incompatibility may occur during blood transfusion reactions of older people. For purposes of this article, we will discuss ABO Incompatibility of the newborn.
In contrast to an Rh Incompatibility of the newborn, ABO incompatibility of the newborn does not generally become more severe with subsequent pregnancies.
Blood Types and ABO Incompatibility:
To understand ABO Incompatibility, we must first touch upon the different blood types: A, B, AB, and O, differentiated by the collection of antibodies on the surface of the red blood cell.
- Type A Blood has Type A Antigen
- Type B Blood has a Type B Antigen
- Type AB has both A and B Antigens
- Type O Blood contains no antibodies on the surface of the red blood cells
If maternal-fetal antibodies commingle, it can launch a maternal immune response, thus creating antibodies that attack the foreign (or fetal) red blood cells.
What Are The Risk Factors Associated With ABO Incompatibility?
There are several risk factors associated with ABO incompatibility:
- Maternal blood type is O, while fetal blood type is A, B, or AB.
- Fetal-maternal hemorrhaging, allowing the blood of the fetus to commingle with that of the mother.
- Trauma to the abdomen that may lead to hemorrhaging.
What Causes ABO Incompatibility?
- During a pregnancy, mixing of maternal and fetal blood doesn’t occur very often – the blood circulation of both mother and fetus are separated by the placental barrier, which does not often allow blood to commingle. However, other things, such as oxygen, carbon dioxide, nutrients, drugs, and certain viruses can pass through the placental membrane.
- During pregnancy, maternal antibodies are transported via the placenta into the fetal circulation. This provides the newborn, who is born with an immature immune system, with invaluable maternal antibodies, which boosts the chance of fetal survival outside of the womb.
- The downside of this survival mechanism occurs when blood manages to cross the placental barrier and maternal antibodies target fetal red blood cells and can lead to ABO Incompatibility, a relatively mild form of hemolytic disease of the newborn.
- Sometimes, however, circumstances allow the two blood types to commingle. If maternal-fetal blood does manage to mingle in a mother who has one type of blood, pregnant with a fetus with a different type of blood, antibodies against the foreign blood are created.
- Unfortunately, these antibodies often pass through the placental barrier and into fetal circulation, where they can cause the destruction of some of the growing fetuses red blood cells.
- The destruction of fetal red blood cells by these antibodies leads to an increase of bilirubin – a waste product of red blood cells normally excreted by the liver – in fetal blood circulation.
- As a result, excess amounts of bilirubin can easily overwhelm the liver of a neonate and lead to a condition called neonatal jaundice.
What is Newborn Jaundice?
Newborn Jaundice is caused by the buildup of excess bilirubin in the bloodstream of the newborn. Newborns are born with immature livers, and conditions like ABO Incompatibility, which causes excess bilirubin to build up in the bloodstream, can lead to newborn jaundice. While most cases of jaundice resolve on their own, newborn jaundice may require medical intervention to properly resolve.
What Are The Complications of ABO Incompatibility?
While ABO Incompatibility is not generally as dangerous as other types of hemolytic diseases of the newborn, there are complications that can be caused by this disorder. Complications of ABO Incompatibility may include:
Newborn Jaundice: most babies who have ABO incompatibility are born with higher than normal levels of bilirubin which can lead to newborn jaundice. Newborn jaundice may or may not require medical intervention to resolve.
Anemia: many newborns who are affected by ABO incompatibility may develop issues with anemia after several weeks. This anemia is due to the increased amounts of a breakdown of the red blood cells in response to maternal antibodies. These antibodies may persist in the newborn’s body for several weeks following delivery. This may necessitate laboratory blood studies to ascertain how anemic the newborn is.
How Is ABO Incompatibility Diagnosed?
Normal prenatal blood screenings do not generally test for ABO incompatibility as during pregnancy, antibody levels do not often properly correlate with any type of ABO Incompatibility. Thus, there is no way to predict or prevent ABO Incompatibility.
There are two options, pre-delivery, for determining whether a baby has developed ABO incompatibility during pregnancy:
- Cord blood testing – mothers with type O blood with fathers who have blood types of A or B are often tested. If the baby is born with type A or type B blood, direct antiglobulin tests (DAT) are performed and the infant can be followed to see if he/she develops anemia or jaundice.
- Screen any baby who appears significantly jaundiced – especially if jaundice occurs within 24 hours of birth.
Treatment of ABO Incompatibility of the Newborn:
The most frequent complication of ABO incompatibility is newborn jaundice, which occurs when there’s a buildup of an orangish-red substance in the blood called bilirubin that’s produced when red blood cells break down naturally. If more red blood cells are broken down at one time than normal, it will deposit fatty tissue under the skin, causing the yellowish hue of the skin and whites of the eyes that are the tell-tale symptom of jaundice. Most cases of newborn jaundice are treated by simply feeding the baby more, which results in a quicker breakdown in bilirubin.
While ABO Incompatibility does not generally symptoms that require major medical treatment, treatment options can include the following:
Phototherapy (anywhere from at-home to in the hospital for more severe cases of newborn jaundice) to treat any newborn jaundice involves putting the newborn under special lights which will breakdown the bilirubin in the baby’s body more quickly.
Antihistamines to treat allergic reactions (if they occur)
Steroids to reduce swelling and inflammation.
Exchange Transfusion, replacing fetal blood with donated blood, is only performed in extreme cases and in specialized medical centers.
It’s important to note that the anemia that may be caused by ABO Incompatibility of the newborn is often negligible, and requires no treatment.
Last audit 6/2018 BSH