The presence of an RhD positive fetus in an RhD negative pregnant woman can cause hemolytic disease of fetus/newborn (HDFN) in future pregnancies. The mother’s antibodies can cross the placenta into the fetal blood stream and induce hemolysis and anemia to a RhD positive fetus. Currently all RhD negative pregnant woman are provided with antenatal anti-D immunoglobulin during the course and post pregnancy as a prophylaxis irrespective of fetus RhD genotype.
However, many RhD negative pregnant women do not require antenatal anti-D immunoglobulin if the fetus is RhD negative. Knowing the fetal RhD genotype during pregnancy is essential to identify RhD-negative pregnant woman who do specifically need targeted or systematic prophylaxis with antenatal anti-D Ig.
It has been demonstrated that the plasma from a pregnant woman contains an increasing concentration of fetal DNA as gestation progresses. From 11th week in gestation the Fetal RhD genotype in the context of Rh negative pregnant woman can be detected using the Free DNA Fetal Kit RhD. Performed with a maternal blood sample from Rh negative pregnant woman, this test avoids unnecessary injections of antenatal anti-D immunoglobulins through the course of pregnancy for non-alloimmunized RhD negative pregnant patients, if the fetus has a Rh negative genotype. This is an important test which should be accessible for all RhD-negative pregnant women.
The presence of the fetal RhD gene in the mother’s plasma sample is detected through multiplex Real Time PCR (rtPCR) on 3 distinct sequences on the RHD gene: exons 5, 7 and 10, making it possible to detect significant variants of the RHD gene. The amplification of all three exons indicates the presence of a fetus with RHD positive genotype.
The extraction of DNA from maternal blood plasma samples and amplification of three exons of the RhD gene have been validated on commonly used automated extraction equipment and real-time PCR machines.
The kit is exclusively dedicated to the determination of the RhD fetal genotype and does not allow any other diagnosis such as sex of fetus for example.