Maternal alloimmunizationAlloimmunization When a person’s immune system develops antibodies against foreign antigens from the same species—such as when an Rh-negative mother’s body forms antibodies against her baby’s Rh-positive red blood cells. occurs when the maternal Rh-negativeRh-Negative A blood type trait that means your red blood cells lack the Rh(D) antigen. blood and fetal Rh-positiveRh-Positive A blood type trait that means your red blood cells have the Rh(D) antigen. blood come into contact, which can occur at any time during pregnancy or delivery. This triggers the mother’s immune system to develop antibodiesAntibody A protein made by the immune system that recognizes and attacks foreign substances, such as bacteria, or in HDFN, fetal red blood cells carrying incompatible antigens. that cross the placenta and attack the fetus’s red blood cells.
Alloimmunization can occur as the result of abdominal trauma, fetal-maternal hemorrhage, amniocentesis, chorionic villus sampling (CVS), surgery, miscarriage, ectopic pregnancy and birth. This can lead to severe anemiaAnemia A condition that occurs when the body doesn’t have enough healthy red blood cells to carry oxygen to its tissues. In HDFN, anemia occurs when maternal antibodies destroy fetal red blood cells. in the fetus, with possible life-threatening complications if not urgently treated.
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 (RhRh factor A protein or antigen found on red blood cells. When an Rh-negative mother carries an Rh-positive fetus, her immune system may make antibodies that attack the fetus' red blood cells.) factor (Rh-positive or Rh-negative) during pregnancy.
When do maternal antibodies cross the placenta?
Maternal antibodies can cross the placenta at any time following alloimmunization, but it occurs mostly in the second or third trimester. When they cross the placenta, the maternal antibodies attack the fetus’s red blood cells, progressively destroying them.
Learn more about HDFN causes and risk factors
As they break down, the fetus develops anemia. Severe anemia decreases the capacity of the blood to carry oxygen around the body, which can lead to heart failure. This also increases the risk of developing complications such as fetal hydrops or extensive swelling in the baby’s tissue and organs due to the build up of fluid.
From alloimmunization to HDFN
In pregnancies at risk of HDFN, maternal alloimmunization is diagnosed with an Indirect Coombs Test or Indirect Agglutination Test (IAT). Following diagnosis, the pregnant patient will be closely monitored, with regular Doppler ultrasounds and blood tests. The blood tests track the titer levels of antibodies in the mother’s blood. If they rise to critical levels, the fetus is at increased risk.
The Dopplers are performed every one to two weeks to check if the fetus’ organs are enlarged and to measure the flow of blood to the brain. If the flow is too fast, the baby is anemic and therefore has HDFN. Cordocentesis, also known as umbilical blood sampling, can be performed to confirm HDFN if the Doppler results show an increase in blood flow. It can also determine the severity of HDFN in the fetus.
Treatment of HDFN in a fetus
Intravenous immunoglobulin (IVIG) has been shown to delay the onset of severe fetal anemia, and the need for Intrauterine blood transfusions (IUTIntrauterine transfusion A procedure that delivers donor red blood cells to the fetus through the umbilical vein to treat severe anemia caused by HDFN.) as well as a lower rate of hydrops and a later gestation age at delivery. Early delivery by cesarean is often required to remove the baby from the ongoing damage inflicted by the maternal antibodies and to provide urgent medical treatment to the newborn.
