During pregnancy, the mother’s and baby’s blood doesn’t usually mix. However, sometimes, small amounts of the baby’s blood cells can leak into the mother’s bloodstream. If the mother’s immune system recognizes these cells as foreign, it may produce antibodies against them. This is called sensitization. The most common cause of sensitization is a blood type incompatibility between the mother and baby.
Certain combinations of blood types between mother and baby can trigger an immune response in the mother. This could lead to conditions like hemolytic disease of the newborn (HDN) which can be dangerous for the baby. Knowing your blood type and your partner’s blood type can help determine the risk of blood type incompatibilities during pregnancy.
Background on Blood Types
Human blood contains antigens – substances that can trigger an immune response if the body encounters unfamiliar antigens. The two most important antigens are the ABO antigens and the Rh antigen. Based on the presence or absence of these antigens, a person’s blood type is classified as:
- A – Has A antigens on red blood cells (RBCs), but no B antigen
- B – Has B antigens on RBCs, but no A antigen
- AB – Has both A and B antigens on RBCs
- O – Has neither A nor B antigens on RBCs
In addition to this, a person’s blood is either Rh positive (has the Rh antigen) or Rh negative (does not have the Rh antigen). So blood types are often written with the ABO type and Rh status – like A positive or O negative.
When someone is exposed to an antigen not present in their own blood, they can produce antibodies against that foreign antigen. For example, a person with A positive blood would have anti-B antibodies against the B antigen.
During pregnancy, there is sometimes mixing of blood between the mother and baby. If this exposes the mother to an antigen found on the baby’s blood cells, but not her own, she can produce antibodies against it. This is called sensitization.
Blood Type Compatibility Concerns
The two main blood type compatibility issues that can sensitise a mother during pregnancy are:
ABO incompatibility
This occurs if the mother and baby have different blood types based on the ABO antigens. For example:
- Mother is blood type O, baby is blood type A
- Mother is blood type B, baby is blood type A
In these cases, the mother does not have the same ABO antigens on her red blood cells as the baby. Exposure to the baby’s RBC antigens leads to production of antibodies.
ABO incompatibility is most likely to cause HDN if the mother’s blood type is O. This is because type O blood has anti-A and anti-B antibodies.
Rh incompatibility
This can occur if the mother is Rh negative and the baby is Rh positive. For example:
- Mother is A negative, baby is A positive
- Mother is O negative, baby is O positive
Since the mother lacks the Rh antigen, exposure to the baby’s Rh positive blood can lead to anti-Rh antibodies.
Rh incompatibility is the most common cause of HDN. It can occur even in the first pregnancy if there is mixing of blood, but is more likely to cause issues in subsequent pregnancies.
Risk of HDN Based on Blood Types
Hemolytic disease of the newborn occurs when maternal antibodies produced from sensitization end up crossing the placenta. This attacks the baby’s ‘foreign’ RBC antigens.
HDN ranges from mild to severe. Complications can include:
- Anemia due to RBC destruction
- Jaundice from the breakdown of hemoglobin
- Swelling and fluid buildup
- Heart failure and circulatory shock in severe cases
The highest risk combinations for HDN are:
Rh incompatibility
- Mother is Rh negative, baby is Rh positive – Severe HDN risk
This is because the mother mounts a strong immune response to the Rh antigen. The risk increases in subsequent pregnancies.
Type O mothers
Mothers with O blood type have higher chances of ABO incompatibility with potential for HDN:
- Mother is O, baby is A – Moderate HDN risk
- Mother is O, baby is B – Moderate HDN risk
- Mother is O, baby is AB – Maximum HDN risk
This is due to the naturally occurring anti-A and anti-B antibodies in type O mothers.
Blood Type Testing
To assess the risk of blood type incompatibilities, the mother’s and father’s blood types should be tested before or early in pregnancy:
- ABO typing – Determines ABO blood group (A, B, AB, or O)
- Rh typing – Detects presence or absence of Rh antigen
Prenatal paternity testing can also be done to confirm the baby’s Rh status if the biological father is known.
If results show a concerning mismatch, the mother’s blood may be periodically screened for antibodies during pregnancy. Ultrasound assessments of the baby may also be done for signs of anemia.
Treatment
There are treatments available if blood type incompatibility is detected:
Rho(D) immune globulin
This medication can prevent sensitization in Rh negative mothers. It works by binding Rh antibodies so they don’t react to the baby’s blood. It is given around week 28 of pregnancy and within 72 hours after delivery.
Intrauterine blood transfusion
This procedure is done if the baby develops severe HDN anemia. Blood matched to the baby’s blood type is transfused into the umbilical cord.
Early delivery
If HDN is advanced and causing critical issues, early delivery may be induced. Care is taken to mature the baby’s lungs first with corticosteroids.
Prevention
When expecting, take these steps to prevent HDN:
- Get ABO and Rh blood typing done early
- Ensure Rh negative mothers receive Rho(D) injections at the right times
- Avoid procedures that may cause mixing of blood between mother and baby
- Get regular antibody screening tests if at high risk
- Evaluate baby’s condition with ultrasound tests periodically
Prompt detection and treatment of blood type incompatibility protects the baby from the harms of HDN.
Key Takeaways
- Blood type mismatches like ABO incompatibility and Rh incompatibility can cause HDN.
- The highest risk is seen with an Rh negative mother carrying an Rh positive baby.
- Type O mothers are prone to ABO incompatibility with babies of other blood types.
- Testing mother’s and father’s blood type early in pregnancy helps assess HDN risk.
- Treatments like Rh immune globulin shots and intrauterine transfusions can prevent or manage HDN when caught early.
Conclusion
Blood type compatibility between mother and baby is an important consideration in pregnancy. Certain combinations like an Rh negative mother carrying an Rh positive baby or a type O mother with a baby of a different blood type have an increased risk of sensitization and HDN if preventive steps are not taken. Testing the blood types of parents early on and monitoring for antibodies allows these high-risk situations to be identified and managed proactively with treatments like Rh immune globulin. This protects the baby from HDN and allows for the best possible pregnancy outcome. Knowing the blood types of both parents is key to determining compatibility and the risk of HDN.