What is hemolytic disease of the fetus and newborn?
Hemolytic disease of the fetus and newborn (HDFN) is a blood disorder in which the baby’s red blood cells break down quickly, known as hemolysis. This causes the release of a breakdown product, bilirubin, into the baby’s bloodstream as well as the destruction of the red blood cells in the baby’s body.
Blood groups
A person’s blood group (or blood type) is classified based on special antigens on the surface of the red blood cell. The antigens are made of proteins, carbohydrates and/or lipids and vary from person to person. These antigens are inherited by our genes. There are many different antigens on a person’s red blood cells. A small number of these can cause HDFN if they do not match between mother and baby.
There are four major blood groups: A, B, AB, and O.
A person’s red blood cells may also contain a protein called the Rhesus (Rh) factor.
- If a person has the Rh factor, they are RhD positive (Rh+), sometimes people refer to this as a 'positive blood group'.
- If they do not have the Rh factor, they are RhD negative (Rh-), or a 'negative blood group'.
There are many more blood groups beyond the "ABO system" or the "Rh +/- system", however these are the most commonly discussed blood groups.
All babies inherit their blood group from both parents. Sometimes, the baby will have a blood group from their father which is different from their mother.
What causes HDFN?
We all have many circulating antibodies. Antibodies are proteins which act in the immune system. Many antibodies are used to fight infection, while others can target other parts of the body including the antigens on red blood cells.
During pregnancy, some antibodies can travel across the placenta into the baby’s bloodstream. Many of these antibodies provide the baby with some protection against infections after the baby is born. If the baby and mother’s blood group do not match, blood type antibodies can travel across the placenta and attach to the baby’s red blood cells, causing quicker destruction of the red blood cells which leads to HDFN.
HDFN due to ABO incompatibility
The most common reason for HDFN is ABO incompatibility; this may occur when the baby and the mother have incompatible blood groups (e.g., baby has A or B blood group and the mother has O blood group). Antibodies in ABO incompatibility occur naturally in the mother’s body if she is O blood group and then travel across the placenta to the baby. This type of HDFN can range in severity from very mild, even undetectable, to moderate requiring some treatments. It is usually mild, and is rarely severe.
What are the risks to my newborn?
All newborn babies develop some jaundice, which is caused by the breakdown product of fetal red blood cells. Jaundice does not develop in babies before birth as the mother’s blood circulation clears the breakdown product quickly. Jaundice is often seen as yellowing of the skin and eyes in the newborn baby. Babies with HDFN develop higher bilirubin levels than babies without HDFN.
High levels of bilirubin are toxic to the developing brain and can cause a condition called kernicterus. Kernicterus is damage to the brain’s nerve cells and can cause neurological consequences including seizures and can lead to long-term hearing loss and cerebral palsy. This is why treatment is initiated quickly to lower bilirubin levels. Kernicterus is very rare, due to early recognition of risk factors and bilirubin testing.
Newborn babies with HDFN are also at risk of developing anaemia from the destruction of their red blood cells. Anaemia is too few red blood cells, also known as low hemoglobin. People need red blood cells to carry oxygen and provide energy to parts of their body, including their heart and brain. Anaemia is life threatening if the red blood cells are too low. Anaemia can develop in severe cases of ABO incompatibility HDFN.
How is HDFN treated after a baby is born?
After the baby is born, they will have blood tests repeated over several days to determine how the hemolysis is progressing (assessing bilirubin levels and hemoglobin levels if necessary).
Depending on the severity of the jaundice, determined by how elevated the bilirubin levels are, there are a few different treatment options.
- Phototherapy is the most common treatment required and uses a special lamp and/or blanket of blue light to help the baby’s body to get rid of the bilirubin. Phototherapy makes the molecules of bilirubin come together, allowing the kidneys to excrete them out of the body through urine. Usually, babies require this treatment for hours to days.
- If jaundice is severe and phototherapy is not enough to treat it quickly, an exchange transfusion may rarely be needed. Exchange transfusions remove the blood with critically high bilirubin levels and replaces it with donated red blood cells. If anaemia is severe, red blood cell transfusions are sometimes required.
- Other therapies, including intravenous immunoglobulin (IVIg), a plasma-based blood product, can also be considered to dampen the immune process in some instances.
Your health-care team will discuss these treatment options with you if they are needed for your baby.
What happens next?
The antibodies that cause hemolysis are present in the baby for several months, however initial treatment is usually only in the first few days, with ongoing monitoring in case further treatment is required. Over time, the amount of antibodies is reduced and they become less active. This may take several months, so your baby will need follow-up appointments over this period.
When to seek medical attention
You should seek medical attention if your baby:
- develops more jaundice or is very pale
- is very sleepy
- is not feeding well
- develops a high-pitched cry
- has any other concerns