Preliminary results of fetal Rhc examination in plasma of pregnant women with anti-c.

OBJECTIVES: Anti-Rhc antibodies may be the reason for the hemolytic disease of the newborn, therefore, noninvasive Rhc determination is important for pregnancy monitoring. For this purpose, we decided to introduce real-time polymerase chain reaction (PCR) method. METHODS: Blood from 200 donors, plasma and whole-blood from 11 Rhc-negative mothers, as well as blood from fathers and newborns were examined. Rhc sensitivity and specificity were first determined by real-time PCR using genomic DNA from donors. The same Rhc genotyping method was used for fetal Rhc detection in maternal plasma. To confirm the fetal Rhc-negative result, plasma was tested with a panel of biallelic insertion/deletion polymorphisms for the presence of fetal DNA. RESULTS: The c allele assay showed full specificity. The mean Ct value for one copy of c allele diluted in C-negative DNA was determined from extrapolating the correlation curve as 39.9. Full concordance was observed between the fetal Rhc genotypes from maternal plasma and the newborn phenotypes. CONCLUSIONS: Preliminary results show that it is possible to examine fetal c allele of RHCE gene in the plasma of pregnant women with anti-c by means of a noninvasive method. The diagnostic accuracy of the procedure, however, has yet to be confirmed in a larger group.

Noninvasive determination of fetal RHD status by examination of cell-free DNA in maternal plasma.

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 of RHD typing and confirmation of fetal DNA in maternal plasma while RHD was 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 of RHD gene with real-time polymerase chain reaction. The presence of fetal DNA was confirmed by testing SRY and, 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 fetal RHD testing (RHD genotyping plus confirmation of fetal DNA) was 99.6 percent. SRY detection confirmed fetal DNA presence in maternal plasma in all boys, whereas the detection of various polymorphisms in all girls but one. CONCLUSIONS: Fetal RHD genotyping 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%).