HDFN is rare – Be aware – Ask for specialist care

HDFN is a rare pregnancy condition which occurs when the mother’s red blood cells are not compatible with the red blood cells of her unborn baby (the fetus). In cases where they are not compatible, the mother’s immune system sees the baby’s red blood cells as foreign and produces antibodies to fight these, which, in rare cases can cause fetal anemia. Fetal anemia is when the amount of circulating red blood cells and hemoglobin in a fetus fall below normal levels. Because red blood cells transfer hemoglobin and oxygen through the blood to the tissues who need it, fetal anemia can have several adverse effects, including heart complications.

A risk of HDFN should be picked up during routine screening with a blood test. There are many different blood group systems. The ABO and Rhesus (Rh) systems are the most well-known and incompatibilities within these, as well as others, can lead to HDFN.

All women should have their blood group and antibody status determined at the beginning of their pregnancy.

If the mother’s blood group and antibody status indicate a risk of incompatibility with the baby’s, non-invasive fetal genotyping using maternal blood is carried out to confirm this. Paternal testing can be also completed to help identify the level of incompatibility. These tests will also enable identification of the type and extent of incompatibility and guide the course of care for the mother and baby.

Antibody levels should also be monitored throughout the pregnancy. If it is confirmed that the mother is producing antibodies against the baby’s red blood cells, a regular antibody titer test should be undertaken to determine the level of antibodies within her blood and thus, the level of risk to the baby.

With subsequent exposures between the fetus’ and mother’s blood, the levels of antibodies and thus the risk to the fetus may further increase, a process called sensitisation.

If sensitization occurs, the next time the woman is pregnant, her body produces antibodies immediately.

Early engagement with a specialist physician who has knowledge and expertise in HDFN is essential to ensure that the pregnancy is diagnosed accurately, assessed for potential risk and closely monitored throughout this and subsequent pregnancy.

Hemolytic disease of the fetus and newborn (HDFN) is a rare pregnancy condition which occurs when the mother’s red blood cells are not compatible with the fetal red blood cells and this can lead to fetal anemia.
There is a range of severity associated with HDFN ranging from mild to very severe. In the most severe cases, fetal death from heart failure may occur.
If there is an incompatibility between the mother and her baby’s red blood cells, the first pregnancy tends to be unaffected as the mother has not yet been exposed to her baby’s blood. Women may not even be aware of the incompatibility with their newborn!
However, upon exposure to their baby’s blood e.g. during childbirth, mother and baby’s blood can mix. In the case of incompatibility, this may cause the mother to start producing antibodies against the baby’s red blood cells which can be dangerous in subsequent pregnancies. Therefore, it is really important that women are educated on the risk of HDFN starting already from the first pregnancy. For women with RhD incompatibility, preventive therapy can be administered which prevents the mother’s immune system from attacking the fetus.

Additional factors which can affect the severity of the disease include:

• The type of antibody that a mother produces – some types of antibodies carry higher risk than others and some can be treated with a preventive therapy
• Antibody titers – the level of antibodies in the blood should be measured regularly throughout pregnancy as in some cases, higher levels are linked to increased severity and risk of fetal anemia (too low number of red blood cells)
• The number of previous pregnancies affected by HDFN – the severity of HDFN tends to be higher with each subsequent pregnancy

There are many steps that your specialist physicians and their teams can implement to monitor the disease and manage any potential associated risks. Antibody levels should be monitored throughout the pregnancy. Regular ultrasounds of the middle cerebral artery (MCA) Doppler should also be undertaken by a specialist physician to monitor the baby’s blood flow and detect any presence of fetal anemia.

HDFN should be managed by a team of HDFN specialists to ensure continuous monitoring of the mother and baby to determine the risk to the fetus and enable early intervention if needed.