In pregnancies affected by hemolytic disease of the fetus and newborn (HDFN), the mother and the baby have incompatible blood types (ABO) or Rh antigens (most often D, but also c, C, E and e). This is due to the fetus inheriting a blood type or Rh factor from the father not present in the mother.
The mother’s immune system identifies them as foreign and attacks the red blood cells of the fetus. Testing of the father in addition to the standard prenatal screening of the mother can more accurately identify the risk of HDFN occurring.
Learn more about FNAIT testing and diagnosis
Maternal prenatal screening
HDFN is most commonly triggered by the D antigen. To assess the risk of developing HDFN, the pregnant mother will receive an ABO, Rh and antibody screen at her first prenatal visit. A D-negative woman will be carefully monitored and then retested at 28 weeks’ gestation and just before delivery. To reduce the risk of RhD alloimmunization she will receive anti-D immunoglobulin at 28 weeks and within 72 hours of childbirth.
If anti-D antibodies are detected, the fetus is at risk of severe anemia and complications that could potentially lead to fetal death.
Paternal testing
In most cases, paternal testing is not performed unless the mother becomes alloimmunized and develops antibodies. Once the maternal antibody is identified, the father may undergo molecular testing to determine if the antigens correspond.
If this is the case, the next step will be DNA testing to identify if the father is homozygous for the D allele (D/D) or heterozygous (D/d). If he is homozygous the fetus will be Rh-positive, and the maternal antibodies will target the fetus’s red blood cells. If he is heterozygous there is a 50/50 chance of the fetus being Rh-positive or Rh-negative. If the fetus is Rh-negative, there is no risk. The fetus’s blood type can be determined by testing fetal cells taken from the umbilical cord.
The importance of testing
HDFN can have serious and even fatal outcomes for the fetus and newborn if left untreated.
The benefits of prenatal maternal testing include:
- An early risk assessment
- Reinforced care and monitoring throughout pregnancy
- Preventive measures during pregnancy
- Early detection and intervention if HDFN develops
The benefits of paternal testing include:
- More accurately determining the level of risk
- In some cases, eliminating the need for anxiety and medical intervention
When performed as a complement to maternal testing, paternal testing contributes to ensuring the best treatment approach during pregnancy and post-delivery.
