In hemolytic disease of the fetus and newborn (HDFN), maternal sensitization usually occurs in the first pregnancy, with second and subsequent pregnancies at greater risk of the fetus developing HDFN. While there is a recognized risk of HDFN developing, specialized maternal fetal care will also be on hand to ensure close monitoring, early diagnosis and timely medical intervention during pregnancy.
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.
Prenatal screening for HDFN
The risk for HDFN is detected in first pregnancies as part of standard prenatal screening at the first prenatal visit (usually eight to 12 weeks gestation), in a blood test that screens for ABO/Rh typing and antibodies. Sensitization may or may not occur in the first pregnancy, but the risk remains. First pregnancies at risk of HDFN are therefore treated as high-risk.
Maternal sensitization
Maternal sensitization occurs when the pregnant mother’s blood is exposed to her fetus’s blood, which is incompatible due to the Rh factor or blood group inherited from the father. T
he antibodies that the pregnant mother’s immune system develops against the fetus’s red blood cells during the first pregnancy stay in her system and will also impact subsequent pregnancies. Sensitization can occur during pregnancy, miscarriage or delivery. In most cases, HDFN has been shown to be more severe with each subsequent pregnancy.
Rh incompatibility
In most cases, HDFN is caused by anti-D antibodies, developed by the Rh-negative mother against her Rh-positive fetus. While it can occur in first pregnancies, in subsequent pregnancies, the risk is higher.
ABO incompatibility
HDFN can also be caused by ABO blood group incompatibility, which is a milder version of the disease. In subsequent ABO-affected pregnancies, the risk is not as high as for Rh-affected pregnancies.
Managing a subsequent pregnancy affected by HDFN
When HDFN is diagnosed in the fetus or newborn of a first pregnancy, this information is vital when planning a second pregnancy. It will inform prenatal care and provide the opportunity to proactively approach the risk of HDFN developing.
A subsequent pregnancy at risk of HDFN will require the care of a maternal fetal specialist and be monitored weekly by ultrasound and blood tests. In later pregnancies, when antibodies already exist, the risk is that they will cross the placenta and attack the fetus’s red blood cells early in the pregnancy.
The administration of intravenous immunoglobulin (IVIG) treatment early in high at-risk pregnancies has been associated with later onset of fetal anemia resulting from HDFN. It can also lead to the fetus requiring intrauterine transfusions (IUT) – an effective but invasive procedure – at a later gestational age, which lowers the risks.
