Erythroblastosis fetalis, also known as Hemolytic Disease of the Fetus and Newborn (HDFN), is a serious blood disorder affecting a developing fetus or newborn. It arises from an incompatibility between the blood types of a pregnant individual and their fetus, leading to the destruction of the baby’s red blood cells.
Understanding the Underlying Cause
The primary cause of erythroblastosis fetalis is Rh incompatibility, often called Rh disease. The Rh factor is a specific protein found on the surface of red blood cells; individuals are either Rh-positive (possessing the protein) or Rh-negative (lacking it). If an Rh-negative mother carries an Rh-positive baby, her immune system may perceive the baby’s Rh-positive red blood cells as foreign substances. This can happen when a small amount of fetal blood enters the mother’s bloodstream, typically during pregnancy or at delivery.
Upon exposure, the mother’s immune system can produce antibodies against the Rh factor, a process known as Rh sensitization. While this sensitization usually does not affect the first Rh-positive pregnancy because it takes time for antibodies to form, it poses a risk to subsequent Rh-positive pregnancies. Once formed, these maternal antibodies, specifically immunoglobulin G (IgG) antibodies, can cross the placenta into the fetal circulation. There, they attach to and destroy the baby’s Rh-positive red blood cells, leading to hemolysis.
Although less common and generally milder, ABO incompatibility can also cause hemolytic disease in newborns. This occurs when a mother with blood type O carries a fetus with blood type A or B. Unlike Rh incompatibility, ABO incompatibility can sometimes affect a first pregnancy because mothers with type O blood may already have naturally occurring antibodies that can cross the placenta. However, the A and B antigens on newborn red blood cells are typically weakly expressed, making the condition less severe.
Impact on the Fetus and Newborn
When maternal antibodies attack the fetal red blood cells, it leads to their destruction and hemolysis. This results in a range of health problems for the fetus and newborn. The most direct consequence is anemia, a reduction in healthy red blood cells, which are responsible for carrying oxygen throughout the body. Severe anemia can compromise oxygen delivery to fetal tissues and organs.
As red blood cells break down, a yellow pigment called bilirubin is produced. The fetal liver and placenta usually process this bilirubin, but rapid destruction of red blood cells can overwhelm these systems, leading to a buildup of bilirubin in the baby’s blood. This excess bilirubin causes jaundice, characterized by yellowing of the skin and whites of the eyes. Uncontrolled, high levels of bilirubin can be damaging, especially to the brain.
Hydrops fetalis is a severe complication involving extensive fluid accumulation and swelling in various parts of the fetus’s body, including the skin, and around the heart, lungs, and abdomen. This condition is a sign of severe anemia and heart failure in the fetus. If not treated promptly, severe jaundice can progress to kernicterus, a rare but serious form of brain damage caused by bilirubin accumulating in brain tissues. Kernicterus can lead to long-term neurological complications, including developmental disabilities and hearing loss.
Diagnosis and Prevention
Diagnosis of Rh incompatibility typically begins with routine maternal blood tests early in pregnancy. These tests determine the mother’s Rh factor and screen for antibodies. An indirect Coombs test is performed to detect if the mother has developed antibodies against Rh-positive red blood cells. If antibodies are detected, their levels are monitored throughout the pregnancy to assess the risk to the fetus.
Fetal monitoring also includes ultrasounds, which can detect signs of anemia or hydrops fetalis by measuring blood flow in the fetal middle cerebral artery. This assessment helps determine if the fetus is experiencing significant red blood cell destruction, allowing for timely interventions.
The primary method of preventing Rh sensitization and erythroblastosis fetalis is the administration of Rh immunoglobulin (RhIg), commonly known as RhoGAM. RhoGAM is a medication made from human plasma that contains antibodies against the Rh factor. When given to an Rh-negative mother, it “fools” her immune system into not producing its own antibodies by clearing any Rh-positive fetal red blood cells that may have entered her bloodstream. This prevents her from becoming sensitized.
RhoGAM is typically administered around 28 weeks of pregnancy and again within 72 hours after the birth of an Rh-positive baby. It is also given after any event that could cause fetal and maternal blood to mix, such as miscarriage, abortion, ectopic pregnancy, or certain prenatal procedures. The widespread use of RhoGAM has significantly reduced the incidence of Rh-induced hemolytic disease, making it rare in developed countries.
Treatment Approaches
For cases where erythroblastosis fetalis develops, medical interventions aim to manage the condition and minimize harm. If severe fetal anemia is detected during pregnancy, intrauterine blood transfusions (IUTs) may be performed. This procedure involves transfusing red blood cells directly into the fetus, often into a vein in the umbilical cord, to correct the anemia. IUTs can improve outcomes for affected fetuses and may be repeated every few weeks until the baby is mature enough for early delivery.
After birth, treatment for affected newborns depends on the severity of their symptoms. Phototherapy is a common treatment for jaundice, where the baby is placed under special lights that help convert bilirubin into a form that the body can more easily excrete. This light therapy helps reduce bilirubin levels and prevent kernicterus. The baby’s skin is exposed to as much light as possible, with their eyes protected.
In severe cases of anemia or high bilirubin levels that do not respond to phototherapy, an exchange transfusion may be necessary. This procedure involves slowly removing small amounts of the baby’s blood and replacing them with donor blood. An exchange transfusion helps remove antibody-coated red blood cells and excess bilirubin while also correcting anemia. Additionally, intravenous immunoglobulin (IVIG) may be given to help protect the baby’s red blood cells from further destruction by maternal antibodies.