In pregnancies at risk of developing hemolytic disease of the fetus and newborn (HDFN), Rh immunoglobulin (RhIG) is standard procedure to potentially prevent it from developing or becoming more serious.
It is administered in two doses to prevent the mother’s sensitization, also known as alloimmunization, to her baby’s Rh-positive red blood cells. Without RhIG, the fetus is at risk of developing HDFN, with potentially life-threatening symptoms such as anemia, hydrops fetalis, cardiac arrest and in some cases, fetal death.
What is HDFN?
Hemolytic disease of the fetus and newborn (HDFN) is an immune-mediated red blood cell disorder that occurs when a baby’s RBCs break down quickly, which is called hemolysis. HDFN is caused by a mismatch between a mother’s and her baby’s blood type (A, B, AB, or O) or Rhesus (Rh) factor (Rh-positive or Rh-negative) during pregnancy.
How does a pregnant person become sensitized?
Prenatal blood type and factor screening will determine if the pregnancy is at risk of developing HDFN. If a mother is Rh-negative and the father Rh-positive, the pregnancy will be considered ‘at risk’. If the fetus’s blood comes into contact with the mother’s blood, the mother becomes sensitized. Events during pregnancy such as antenatal bleeding, abdominal injury, chorionic villus sampling and cordocentesis can result in the pregnant mother becoming sensitized.
Once the mother is sensitized, her immune system starts to produce anti-D antibodies that can cross the placenta and attack the red blood cells of the fetus.
How does RhIG prevent HDFN?
RhIG is a human-derived blood product that contains IgG antibodies against the Rh antigen D (RhD). It is given as an injection into the arm or hip to pregnant mothers who are Rh-negative. A first dose of 300 μg is given at weeks 26 or 28 weeks of pregnancy, with a second dose of 300 μg given within 72 hours of birth of a Rh-positive baby. The risk for alloimmunization is at its highest during labor and delivery, with potential consequences for future pregnancies if it occurs.
When RhIG is injected into the pregnant mother, anti-D antibodies bind to the D-positive red blood cells of the fetus and prevent the fetal immune system from generating anti-D antibodies.
Learn more about HDFN treatment and care
What risks are associated with RhIG?
The administration of RhIG is safe for mother and baby, with only minor side effects reported. The most common side effects include fever, headache, chills and pain at the injection site. More serious adverse events are rare but if they do occur, they must be reported to your doctor urgently. They may include nausea, vomiting, blood in urine, increased thirst, loss of appetite or dizziness.
Is RhIG given to every Rh-negative pregnant mother?
A red blood cell antibody cell will be performed before RhIG is administrated. If alloimmunization has already occurred, no doses of RhIG will be given.
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