Blood group incompatibility refers to the mismatch of blood group types and factors between a pregnant mother and her baby. If a mother and her baby don’t share the same blood group or have different Rh factors, there is a significant risk of the mother’s blood developing antibodies that attack her baby’s red blood cells. Without close monitoring and timely treatment, this can lead to hemolytic disease of the fetus and newborn (HDFN).
Each person has a blood group (also known as blood type) of O, A, B or AB and an Rh factor, which is either positive or negative. They are decided by your genes, inherited from your parents.
HDFN is a serious red blood cell disorder that requires urgent treatment. If left untreated, it can be life-threatening for your baby.
Read more about HDFN causes and risk factors
Blood groups in the ABO system
There are 4 blood groups in the ABO system, with O being the most common, followed by types A and B. ABO blood typing will be carried out before any blood transfusions
to ensure the correct blood type is transfused and during pregnancy to manage any potential risk of ABO incompatibility.
Rh-factor system
The Rh factor is found on the surface of red blood cells. If you have this inherited protein in your red blood cells, you are Rh-positive. If you don’t, you are Rh negative.
Problems can arise if Rh proteins are mixed, such as during a blood transfusion or pregnancy and birth when the mother and baby have different Rh factors.
ABO incompatibility during pregnancy
The most common form of ABO incompatibility during pregnancy occurs when the mother has O type blood, and her baby has B, A, or AB blood type. More rarely, it can occur when a mother has a B blood type and the baby has an A blood type. This incompatibility can trigger an immune response in the mother, and as a result, her immune system will develop antibodies to attack her baby’s red blood cells. This is called fetal sensitization and can lead to HDFN.
While the risk of ABO incompatibility is found in 12 to 15% of pregnancies, only 3 to 4% of fetuses are sensitized, with an incidence of symptomatic HDFN less than 1% in newborns. This is because ABO group antibodies are usually too large to cross the placenta and reach the baby’s blood. However, HDFN can develop post-delivery, with possible symptoms in the newborn of mild jaundice and anemia.
The severity of HDFN due to ABO incompatibility is less than when it arises from RH incompatibility.
Rh incompatibility during pregnancy
If a pregnant mother is Rh-negative and the baby’s father is Rh-positive, there is a risk that the baby will be Rh-positive, as the Rh-positive gene is more dominant. Rh incompatibility is the most common cause of HDFN.
If this risk is identified during prenatal blood screening, you will be carefully monitored throughout your pregnancy and delivery. You will receive injections of anti-D immunoglobulin at 28 weeks of your pregnancy and within 72 hours of giving birth. This will also reduce the risk of developing complications in subsequent pregnancies.
If your baby is diagnosed with HDFN in utero, early detection and prompt treatment are essential. Treatment during pregnancy includes intravenous immunoglobulin, intrauterine transfusion and early delivery. Post-delivery, jaundice and anemia in the newborn will be treated with phototherapy and blood transfusion and exchange transfusion in serious cases.
