In pregnancies at risk of developing hemolytic disease of the fetus and newborn (HDFN), invasive procedures such as chorionic villus sampling can cause the fetus’s red blood cells to come into contact with maternal blood. Alloimmunization occurs, meaning the mother’s body develops antibodies against the fetus’s red blood cell antigen, which could eventually lead to the onset of HDFN in the fetus.
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.
What is chorionic villus sampling?
Chorionic villus sampling (CVS) is a prenatal diagnostic test used in pregnancies with a higher risk of genetic or chromosomal conditions. Usually performed at around 10 to 13 weeks, it helps identify rare conditions such as Down syndrome, trisomy 18, trisomy 13, cystic fibrosis and other genetic disorders or abnormalities. It is not part of standard prenatal testing and is only offered in certain circumstances, such as a family history of a genetic disorder and if the pregnant woman is older than 35.
It is an invasive medical procedure where a long thin needle, guided by ultrasound, is inserted into the mother’s abdomen and uterus to collect a small sample of placental tissue, called the chorionic villi. This sample is tested in a genetics laboratory, with results available within one to two weeks.
The CVS procedure is generally considered safe, with a low risk of complications such as infection or miscarriage.
If any genetic or congenital health conditions are detected, you will be supported by a genetics counselor.
What is alloimmunization in HDFN?
If fetal blood cells are accidentally spilled into the maternal bloodstream, this causes alloimmunization in the pregnant mother. Due to an incompatibility in blood types or factors, her immune system identifies the fetus’s blood as a possible threat and produces antibodies against the antigens on her fetus’s red blood cells. They cross the placenta, attack the fetal blood and cause HDFN.
How does CVS cause HDFN?
Standard prenatal testing will identify the risk of HDFN developing in the fetus or newborn as a result of blood type or factor incompatibility and the pregnancy will require close monitoring by ultrasounds and regular blood tests.
The risk of a CVS procedure to a pregnancy at risk of HDFN comes from the potential for the fetus’s blood to mix with the mother’s blood as a result of the sample taken from the placenta.
In pregnancies at risk of HDFN, non-invasive testing is the preferred option. However, if CVS is performed, all precautions are taken to avoid possible maternal alloimmunization. In cases of RhD incompatibility, an RhD immunoglobulin injection will be given following the procedure to help prevent alloimmunization.
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