Noninvasive fetal RhD genotyping.

Immunization against RhD is the major cause of hemolytic disease of the fetus and newborn (HDFN), which causes fetal or neonatal death. The introduction of postnatal immune prophylaxis in the 1960s drastically reduced immunization incidents in pregnant, D-negative women. In several countries, antenatal prophylaxis is combined with postnatal prophylaxis to further minimize the immunization risk. Due to lack of knowledge of the fetal RhD type, antenatal prophylaxis is given to all D-negative women. In the European population, approximately 40% of pregnant women carry a D-negative fetus and are thus at no risk of immunization. Noninvasive fetal RhD genotyping enables antenatal prophylaxis to be targeted to only those women carrying a D-positive fetus to avoid unnecessary treatment. Based on an analysis of cell-free fetal DNA from the plasma of pregnant women, this approach has recently undergone technical improvements and rapid clinical implementation. As a screening assay, the sensitivity is >99.3% from a gestational age of approximately 10-11 weeks. In addition, fetal RhD genotyping is widely used to assess the risk of HDFN in anti-D immunized women.