The determination of the fetal D status from maternal plasma for decision making on Rh prophylaxis is feasible.
BACKGROUND
Noninvasive fetal RHD genotyping might become a valuable tool in decision making on antenatal Rh prophylaxis, which is currently in routine practice for all D- pregnancies in several countries. This study provides a large-scale validation study of this technology to address questions concerning feasibility and applicability of its introduction into clinical routine.


METHODS
Real-time polymerase chain reaction (PCR) targeting RHD Exons 5 and 7 was applied for the detection of fetal-specific RHD sequences in maternal plasma. A total of 1113 women in 6 to 32 weeks (median, Week 25) of pregnancy were recruited. All of them were serologically typed as D- according to current German guidelines. DNA was extracted via a spin-column method and a novel automated approach using magnetic tips. Real-time PCR results were compared with postnatal serology and discrepancies further elucidated by DNA sequencing from a newborn's buccal swab.


RESULTS
Sensitivities of fetal RHD genotyping were 99.7 percent (spin columns) and 99.8 percent (magnetic tips), thus comparable with serology (99.5%). The detection of weak D variants was more reliable by real-time PCR. Specificities of fetal RHD genotyping were 99.2 percent (spin columns) and 98.1 percent (magnetic tips), which is lower than serology (>99.7%). Automation achieved significantly higher yields of cell-free fetal DNA.


CONCLUSIONS
This prospective clinical trial revealed that routine determination of the fetal D status from maternal plasma is feasible. Noninvasive fetal RHD genotyping can be considered as sensitive as the traditional postnatal serologic assay.
Müller
Sina P
SP
Department of Transfusion Medicine, Department of Human Genetics, University Medical Center, Göttingen, Germany.
Bartels
Iris
I
Stein
Werner
W
Emons
Günther
G
Gutensohn
Kai
K
Köhler
Michael
M
Legler
Tobias J
TJ
D000328:Adult; D001788:Blood Grouping and Crossmatching / Q000379:methods*; D003199:Computer Systems; D004247:DNA / Q000097:blood / Q000302:isolation & purification; D003657:Decision Making; D004899:Erythroblastosis, Fetal / Q000517:prevention & control; D005260:Female; D005312:Fetal Blood / Q000276:immunology*; D005331:Fetomaternal Transfusion; D005838:Genotype; D006801:Humans; D007231:Infant, Newborn; D007518:Isoantibodies; D016133:Polymerase Chain Reaction / Q000379:methods; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D011446:Prospective Studies; D012204:Rh-Hr Blood-Group System / Q000032:analysis* / Q000235:genetics; D018029:Rho(D) Immune Globulin; D012680:Sensitivity and Specificity; D019564:Unnecessary Procedures
D007518:Isoantibodies; C061961:RHO(D) antibody; D012204:Rh-Hr Blood-Group System; D018029:Rho(D) Immune Globulin; C026410:Rho(D) antigen; D004247:DNA