Routine fetal RHD genotyping with maternal plasma: a four-year experience in Belgium.
BACKGROUND
The objective was to evaluate the diagnostic value of RHD fetal genotyping from the plasma of D- mothers as soon as 10 weeks' gestation in a routine clinical practice in Belgium.


METHODS
A prospective study was conducted between November 2002 and December 2006. DNA extraction was performed in an automated closed tube system. Fetal RHD/SRY genotypes were detected in the plasma of 563 pregnant mothers by real-time polymerase chain reaction (PCR) targeting multiple exons 4, 5, and 10 of the RHD gene and targeting an SRY gene sequence. These were compared to the D phenotypes determined in the 581 babies they delivered.


RESULTS
By combining amplification of three exons, the concordance rate of fetal RHD genotypes in maternal plasma and newborn D phenotypes at delivery was 100 percent (99.8% including one unusual false-positive). The presence of nonfunctional RHD genes and the absence of a universal fetal marker, irrespective of fetal sex, did not influence the accuracy of fetal RhD status prediction. The RHD genotyping from 18 twin pregnancies was also assessed. Five weak D women were excluded from the RHD fetal genotyping prediction. Three discrepant results (0.5%) between predicted fetal genotype and cord blood phenotype were not confirmed by the baby phenotypes from venipuncture blood.


CONCLUSIONS
Prenatal prediction of fetal RHD by targeting multiple exons from the maternal plasma with real-time PCR is highly sensitive and accurate. Over 4 years, this experience has highly modified our management of D- pregnant women.
Minon
Jean-Marc
JM
Department of Laboratory Medicine, the University Department of Fetal Medicine, Centre Hospitalier Régional de la Citadelle, Liège, Belgium. jean.marc.minon@chrcitadelle.be
Gerard
Christiane
C
Senterre
Jean-Marc
JM
Schaaps
Jean-Pierre
JP
Foidart
Jean-Michel
JM
D000465:Algorithms; D001530:Belgium; D004247:DNA / Q000235:genetics; D005091:Exons / Q000235:genetics; D005260:Female; D005838:Genotype; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D009035:Mothers; D010641:Phenotype; D010949:Plasma / Q000378:metabolism*; D011247:Pregnancy; D012204:Rh-Hr Blood-Group System / Q000097:blood* / Q000235:genetics*; D013997:Time Factors
D012204:Rh-Hr Blood-Group System; D004247:DNA