Noninvasive fetal RhD status determination in early pregnancy.

Introduction: The aim of this study was to examine if noninvasive fetal RhD genotyping from maternal blood cell-free fetal DNA performed in the first trimester of pregnancy is accurate enough to propose its routine application to replace usual immunoprophylaxis.

Material And Methods: We carried out a prospective study analyzing fetal RhD genotype in 149 nonimmunized RhD-negative women with single pregnancies between 8 and 13 weeks of gestation. Fetal RhD genotype was detected by quantitative PCR targeting exons 5 and 7. The results were compared with postnatal cord blood phenotype, and discrepancy rates were calculated.

Results: The concordance of fetal RhD genotypes in maternal plasma and newborn D phenotypes at delivery was 98.2%, including 1 false-positive and 1 false-negative result. The specificity and sensitivity of the assay were 97.5% (95% CI 87.1-99.9) and 98.6% (95% CI 92.7-99.9), respectively, and 6.5% of the results were inconclusive. The application of this test in early pregnancy would avoid unnecessary antenatal prophylaxis in about 27% (40/143) of nonsensitized RhD-negative women.

Discussion: Determination of the fetal RhD status from cell-free fetal DNA in maternal plasma in the first trimester of pregnancy is feasible and highly accurate, thus allowing consideration of replacing general routine immunoprophylaxis in the cases of mothers with Rh-negative fetuses.