[Prevention of fetomaternal rhesus-D allo-immunization. Perspectives]

At present, rhesus prophylaxis concerns RhD negative pregnant women, even though 30 to 40% of them are bearing a RhD negative child. Knowing the RhD fetal genotype could change this quite irrational practice of prophylaxis (exposing many more women than needed to blood derived products) without reducing its efficacy. RhD fetal genotype determined on amniotic fluid has an excellent sensitivity. Presence of silent D genes slightly impairs its specificity which remains acceptable. However women have to be informed of possible false positives. Fetal RhD genotyping on maternal blood is more complex. Sensitivity is good from 10 GW and excellent after 15 GW. In case of a first negative result, it is recommended to control fetal RhD on a second sample drawn a few weeks later. Another new perspective for rhesus prophylaxis is the attempt to substitute polyclonal IgG anti-D into human monoclonal IgG anti-D. The main difficulty is to elaborate monoclonal antibodies with a capacity to neutralize RhD positive red blood cells equivalent to those of polyclonal anti-D. A new generation of antibodies is in process and preliminary clinical results are suggesting a possible use of these monoclonal antibodies for future rhesus prophylaxis but long-term follow-up is required to draw further conclusions.