Background: A majority of studies predicting the foetal RhD blood group in free foetal DNA from RhD-negative maternal plasma have been conducted in Caucasian populations, whereas limited data have been accumulated for Asian populations. In this study, we assessed the feasibility of prenatal genotyping of RHD in RhD-negative Chinese pregnant women.
Materials and methods: Cell-free plasma DNA was extracted from 78 RhD-negative Chinese women carrying a singleton foetus (gestation between 14 and 40 weeks). Foetal DNA was confirmed by testing SRY or nine different polymorphic STR loci in the maternal plasma and buffy coat. Foetal RHD exons 5, 7 and 10 and intron 4 were successfully amplified with RQ-PCR. The RHD1227A allele was examined in all RhD-positive individuals. The foetal RHD genotyping results were compared with the infant cord blood serological analysis.
Results: Among the 78 specimens, RHD genotyping results of 70 cases were in complete concordance with serological results from foetal umbilical cord blood. Sixty of these cases were identified as RhD-positive, and 10 cases were typed as RhD-negative. In addition, five cases were 'false-positives', while three cases were considered inconclusive. The detection rate was 89.7% (70/78). In four of the five 'false-positive' cases, the RhDel phenotype was assessed by detecting the RHD1227A allele. Thus, this method yielded a 94.9% (74/78) accuracy rate.
Conclusions: The correct foetal RhD phenotype may be accurately predicted from RhD-negative maternal plasma in Chinese subjects. The RHD1227A allele proved to be an important genetic marker in the RhDel Chinese population.