Reliability and clinical application of fetal RhD genotyping with two different fluorescent duplex polymerase chain reaction assays: Three years' experience

OBJECTIVE: This study was designed to evaluate accuracy and clinical usefulness of fetal RhD genotyping with fluorescent duplex polymerase chain reaction. STUDY DESIGN: Two RhD-specific gene fragments (exon 10 in polymerase chain reaction 1 and exon 7 in polymerase chain reaction 2) were amplified in samples from 213 fetuses. RESULTS: Amplification failed in 0.9% of the specimens, and equivocal results were found in 1.4% of the specimens. Of the analyses, 6.6% had to be repeated. The concordance of genotyping and serotyping was 99.0% for each polymerase chain reaction. False-positive results were noted in 4 fetuses. Concordant findings from both assays indicated the correct serotype for all fetuses. In 44 alloimmunized pregnancies, further invasive procedures were avoided for 5 of the 6 genotypically RhD-negative Fetuses. Only two of 38 RhD-positive fetuses had a hemoglobin level <8 g/dL at first fetal blood sampling. CONCLUSIONS: Fetal genotyping at distinct regions of the RhD gene is reliable and improves the care management of sensitized women.