This post was written by Annie Ilnicki, MT (ASCP) SBBCM, blood bank specialist, Parkview Health.
Knowing the blood types of both mother and baby during pregnancy is crucial to ensuring a safe and healthy delivery. In this post, we'll discuss how differing antigens can impact pregnancy and the importance of early intervention in preventing adverse outcomes caused by incompatible blood types.
What is blood type?
Human blood is typed according to whether certain markers (antigens) are present on the surface of red blood cells and are necessary for determining blood compatibility. The most important antigens are blood group antigens (ABO) and the Rh antigen (also known as D antigen), which is either present (positive, +) or absent (negative, -).
What happens when blood types are incompatible?
People with one blood type may form antibodies when exposed to other blood types. Those antibodies will then react with those other blood types upon additional exposure. When a woman is pregnant, some of the antibodies in her blood can cross through the placenta and into the fetus. There are two types of antibodies that can lead to complications during pregnancy:
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ABO antibodies: These antibodies are naturally occurring and begin developing about four months after birth. For example, if the mom is born with Anti-A,B antibodies, and the fetus is either type A or B, the mother's antibodies could begin coating the fetus's red blood cells.
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Alloantibodies: This type of antibody forms when a human is exposed to other, non-self red blood cells. For example, a woman with Rh-negative blood who has been exposed at least once to Rh-positive blood, from transfusion or a previous pregnancy, may develop alloantibodies. This immune system response may not have impacted the first infant but can cause serious problems during a future pregnancy if the fetus has Rh-positive blood. However, most hospitalized people (>70%) will not make detectible alloantibodies after exposure.
When either of these antibodies crosses the placenta and enters the fetus's bloodstream, it can begin attacking the fetus's red blood cells if they are not similar to the mother's. This reaction sometimes causes Hemolytic Disease of the Fetus and Newborn (HDFN).
The symptoms of HDFN can present as:
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pale skin
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yellowing of the skin (jaundice) or eyes
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very dark urine
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increased fatigue or irritability
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rapid breathing
In more severe cases, it can also cause an enlarged liver and spleen, fluid accumulation and neurologic problems.
Treatment
If red blood cell incompatibility is determined, providers can monitor the fetus's health closely and administer appropriate therapies to prevent further complications.
After the baby is born, if the antibody-red blood cell reaction is strong enough, the blood bank may determine the patient has a positive direct antiglobulin test (DAT). A positive DAT, due to ABO incompatibility, can often be treated by phototherapy and close monitoring.
However, alloantibodies can be much more destructive, sometimes requiring multiple red blood cell transfusions or full red blood cell and plasma exchange transfusions. In some cases, a physician may even transfuse a fetus in utero.
Takeaways
The most important way to combat red blood cell incompatibility is through preparation during prenatal care. Blood incompatibility can be diagnosed with an obstetric panel, which is a group of blood tests and antibody screens done to check the mother's health before and during early pregnancy. Although these exams may not determine the baby's blood type, a primary care physician or obstetrician can take preventive action to lessen the possibility of severe reactions.
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