Preventing Rhesus factor disease
In this video, from our Transfusion Medicine Essentials course, you'll learn how to avoid harm to an unborn child by preventing Rhesus D alloimmunization and hemolytic disease.
Dealing with blood group incompatibilities between mother and child can be daunting! In this video, from our Transfusion Medicine Essentials course, you'll learn how to avoid harm to an unborn child by preventing Rhesus D alloimmunization and hemolytic disease.
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[00:00:00] Rhesus D disease is one form of hemolytic disease of the fetus and newborn. It requires a rhesus negative mother bearing a rhesus positive child. In detail, it occurs after the rhesus negative mother was sensitized by rhesus positive red blood cells in the past, either in a previous pregnancy or by blood transfusion or rarely by needle sharing. If that woman is then pregnant with a rhesus D
[00:00:30] positive child, a tiny amount of fetal RBCs enters the mother's circulation and boosts anti-D IgG antibody production. These IgG antibodies cross the placenta and lead to hemolysis and anemia. The most severe form of rhesus disease is called hydrops fetalis. Here, the fetus develops heart failure with multiple effusions and edema, which is fatal for the fetus. Many countries have implemented programs to prevent rhesus disease
[00:01:00] by preventing sensitization of the mother's immune system in the first place. The program starts with screening all pregnant women at their first prenatal visit for their rhesus antigen as part of their blood group testing as well as your antibody status. Since Rhesus negative mothers might have a rhesus positive child and thus bear the risk of becoming sensitized, all rhesus negative mothers receive an anti-D immunoglobulin prophylaxis to prevent immunization.
[00:01:30] This minimizes the chance of developing hemolytic disease of the fetus and newborn in subsequent pregnancies. Interestingly, we don't know exactly how the prophylaxis works. The prophylaxis contains human anti-D antibodies from pool plasma. Basically, these prophylactic anti-D antibodies bind to the fetal RBCs in the maternal circulation, leading to increased clearance of these cells before the maternal immune system can be activated. A single dose of the anti-D immunoglobulin
[00:02:00] contains enough anti-D to suppress 30 mL of fetal whole blood. That should be enough to counteract normal amounts of fetal-maternal bleeding. It's administered either intramuscularly or intravenously depending on the preparation. The half-life is about 24 days. The first shot is given at 28 weeks of gestation. The second shot is not automatically given to all rhesus negative mothers.
[00:02:30] The second shot is only given to rhesus negative mothers whose newborn tested rhesus positive after simple chord blood explanation. In this case, anti-D prophylaxis should be administered to the mother within 72 hours after giving birth. If the baby turns out to be rhesus negative, there is no need for prophylaxis as there is no danger of sensitization and rhesus disease. An additional shot of anti-D prophylaxis might be given to rhesus negative mothers in situations with high risk of
[00:03:00] increased fetal-maternal bleeding. These situations include abortion or a threatened abortion, fetal death, ectopic pregnancy, invasive in utero procedures, external cephalic version, antenatal vaginal bleeding, abdominal trauma or partial molar pregnancies. In most situations, one single dose of anti-D immunoglobulin will be enough to prevent immunization. When fetal-maternal bleeding of more than
[00:03:30] 30 mL fetal whole blood is suspected, special laboratory tests can estimate the extent of bleeding and determine the adequate dosage. Lastly, when is anti-D prophylaxis not necessary at all? There is no need for anti-D prophylaxis in rhesus-D positive mothers and mothers who were already sensitized from past pregnancies or transfusions or in risk negative mothers who certainly carry a rhesus negative fetus.
[00:04:00] Given that last statement, how would you know for certain that the fetus is rhesus negative? First, if the biological father is known and is definitely rhesus negative then the child can only be rhesus negative as well and prophylaxis is not needed. However, misinterpreted paternity can be a problem. So, I don't recommend relying on this method. The second way to know for certain that the fetus is rhesus negative is by performing cell-free DNA testing. Fetal DNA
[00:04:30] is found in the maternal bloodstream, so one single blood sample from the mother is enough to determine the rhesus-D genotype type of the fetus. This is a very useful method. However, it's still costly and only a few European countries perform this DNA test routinely. To sum up, anti-D prophylaxis programs helped to decrease the incidence of rhesus disease immensely. The correct proceeding can save lives so better stick with it.