If you are managing a pregnancy affected by hemolytic disease of the fetus and newborn (HDFN), you will be screened for alloantibodies. If they are detected, close monitoring of your antibody titers will be required throughout your pregnancy to assess the risk to your baby.
If titers reach critical levels, fetal anemia may occur, which can lead to life-threatening complications for your baby. Early detection, regular monitoring and specialist care are essential to achieve the best outcomes.
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.
What are maternal antibodies and how are they detected?
In women who are pregnant with a baby at risk of developing HDFN, it is critical to know if alloimmunization has occurred. Alloimmunization is found in approximately 1% to 2% of pregnancies.
As part of prenatal screening, ABO and RhD blood group typing is performed, as well as an indirect antiglobulin test (IAT) to check for alloantibodies. If no antibodies are detected, the test will be repeated at 25 weeks’ gestation in Rh-negative pregnant mothers who are at risk of carrying a Rh-positive baby. If the test is positive for IgG antibodies, it confirms that the fetus’s blood has come into contact with the mother’s blood. This activates the maternal immune system to develop antibodies against the fetus’s red blood cells, causing them to break down. Not all cases of alloimmunization progress to HDFN but monitoring the antibody titers will allow proactive treatment if it does.
How are antibody titers monitored and how often?
Once red blood cell alloimmunization is confirmed in the pregnant mother, HDFN can occur in the fetus, leading to fetal anemia and complications such as hydrops fetalis, heart failure and even fetal death.
Blood tests every four weeks will monitor antibody titers until 24 weeks, and then every two weeks until 37-38 weeks. If the titer levels reach 16, this is critical and indicates that the fetus is at risk of HDFN-related fetal anemia.
Implications for care
When antibody titers are high, the fetus requires monitoring by MCA doppler every one to two weeks, which measures blood flow in the brain. If the blood flow is faster, this indicates fetal anemia.
To help delay the onset of fetal anemia earlier in pregnancy, intravenous immunoglobulin (IVIG) can be administered to help protect the fetus’s red blood cells against aggressive maternal antibodies. This also delays the need for the fetus to receive an intrauterine blood transfusion (IUT), which can be a higher risk if performed before 20-22 weeks gestation.
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