Non-invasive fetal RHD genotyping: A Rapid Qualitative Review [Internet]

Excerpt

Non-invasive fetal RhD blood group genotyping, also known as fetal RhD genotyping, is meant to identify Rh compatibility between pregnant persons and their fetus. It offers the potential to avoid unnecessary prenatal treatment or other invasive forms of fetal blood group identification.

Rh blood group incompatibility occurs most often when a pregnant person’s blood type is RhD negative (RhD−) (i.e., lacks the Rh protein on their red blood cells) and the fetus’ blood type is RhD positive (RhD+). Alloimmunization may occur in Rh incompatible pregnancies when a sufficient amount of the fetus’ RhD+ red blood cells cross into the maternal RhD− blood stream during or after childbirth. Alloimmunization is the development of maternal anti-D antibodies as an immune response to the presence of the fetal blood’s foreign antigens. Once these antibodies have been produced in an Rh incompatible pregnancy, the person and pregnancy are referred to as alloimmunized. While alloimmunization during pregnancy rarely affects the first pregnancy, in subsequent pregnancies the antibodies can pass through the placenta to the fetus, which risks causing hemolysis and hemolytic disease of the fetus and newborn (HDFN).

When a pregnant person’s blood type is RhD−, during their first pregnancy they are given prophylactic injections of anti-D Rh-immunoglobulin (RhIG). These injections help prevent alloimmunization and decrease the subsequent risk of developing HDFN (of varying severity). This prophylaxis is given to all RhD− pregnant persons because current standard of care (i.e., routine blood work during pregnancy) is unable to determine the fetus’ RhD status prior to birth. While there are no documented adverse effects of prophylaxis administration in Canada, it is important to note that as a blood product there is always a risk of transmitting infection. Further, as the availability of RhIG is based on the current blood supply (and therefore donations), some healthcare providers have indicated concern regarding its ongoing availability for the RhD− population and advocate thoughtful resource stewardship.