Blood groupBlood group A classification of blood based on inherited markers found on red blood cells. The ABO and Rh blood groups are most common in HDFN. 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 RhRh factor A protein or antigen found on red blood cells. When an Rh-negative mother carries an Rh-positive fetus, her immune system may make antibodies that attack the fetus' red blood cells. factors, there is a significant risk of the mother’s blood developing antibodiesAntibody A protein made by the immune system that recognizes and attacks foreign substances, such as bacteria, or in HDFN, fetal red blood cells carrying incompatible antigens. 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 factorRh factor A protein or antigen found on red blood cells. When an Rh-negative mother carries an Rh-positive fetus, her immune system may make antibodies that attack the fetus' red blood cells., 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-positiveRh-Positive A blood type trait that means your red blood cells have the Rh(D) antigen.. 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 sensitizationSensitization The process by which a mother’s immune system becomes “primed” to recognize and attack fetal red blood cells carrying incompatible antigens. 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 sensitizedSensitization The process by which a mother’s immune system becomes “primed” to recognize and attack fetal red blood cells carrying incompatible antigens., 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 jaundiceJaundice A common symptom of HDFN, jaundice is caused by excess bilirubin and is characterized by a yellow tint to the skin or eyes. and anemiaAnemia A condition that occurs when the body doesn’t have enough healthy red blood cells to carry oxygen to its tissues. In HDFN, anemia occurs when maternal antibodies destroy fetal red blood cells..
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-negativeRh-Negative A blood type trait that means your red blood cells lack the Rh(D) antigen. 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 immunoglobulinIntravenous immunoglobulin A therapy made from donated antibodies that may help reduce the mother’s immune response and protect the fetus. 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 immunoglobulinIntravenous immunoglobulin A therapy made from donated antibodies that may help reduce the mother’s immune response and protect the fetus., intrauterine transfusionIntrauterine transfusion A procedure that delivers donor red blood cells to the fetus through the umbilical vein to treat severe anemia caused by HDFN. 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.
