Non-invasive antenatal determination of fetal blood group in pregnancy care

Abstract

Non-invasive prenatal testing (NIPT) using cell-free fetal DNA in maternal plasma can be used to determine the fetal blood group antigen status for a variety of blood group genes. Knowing what the fetal blood group status is, matters in two different aspects of pregnancy care. For Rh D negative women, the use of antenatal and post-natal administration of prophylactic Rh D immunoglobulin (RhD Ig) has been a game-changer in preventing Rh D allommunisation. At present in Australia, all Rh D negative women are eligible but up to 30–40% of women are in fact carrying an Rh D negative fetus and do not require antenatal RhDIg. The widespread use of NIPT for the RhD gene will allow us to target antenatal RhD Ig to women known to be carrying a D positive fetus, avoiding unnecessary administration, and preserving a scarce resource. For women embarking on pregnancy with an alloantibody capable of causing moderate to severe haemolytic disease of the fetus and newborn (HDFN), knowing the fetal antigen status matters to determine the intensity of pregnancy monitoring. Where the partner is heterozygous, there is a 50% chance of an unaffected pregnancy. In the past, CVS and amniocentesis were the only way to determine fetal antigen status, with such invasive testing likely to boost the maternal antibody response and worsening disease. NIPT enables intense pregnancy monitoring to be better targeted.