Noninvasive determination of fetalRHDstatus by examination of cell‐free DNA in maternal plasma

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Abstract
BACKGROUND:Cell‐free fetal DNA in maternal plasma opens the way for routine risk‐free diagnosis of fetal D status of D– mothers. The focus was on accuracy ofRHDtyping and confirmation of fetal DNA in maternal plasma whileRHDwas not detected.STUDY DESIGN AND METHODS:Plasma DNA was extracted (by manual and/or automatic method) from 255 D– pregnant women and amplified in exons 7 and 10 and intron 4 ofRHDgene with real‐time polymerase chain reaction. The presence of fetal DNA was confirmed by testingSRYand, when negative, by one of 11 different polymorphisms found in the father but not in the mother. The results were compared with the D status of the newborns.RESULTS:After exclusion of 25 cases (10%) because of material shortage, in 230 cases (90%) available for complete study, the predictive value of the procedure of fetalRHDtesting (RHDgenotyping plus confirmation of fetal DNA) was 99.6 percent.SRYdetection confirmed fetal DNA presence in maternal plasma in all boys, whereas the detection of various polymorphisms in all girls but one.CONCLUSIONS:FetalRHDgenotyping from maternal plasma may be used with confidence, although additional polymorphisms for confirmation of fetal DNA should be included for 100 percent predictive value (instead of 99.6%).