Management of platelet and RhD maternal immunizations by PCR phenotypings after early amniocentesis

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.

Fetal Rhesus D genotyping on amniocytes in alloimmunised pregnancies using fluorescence duplex polymerase chain reaction

OBJECTIVE

1. To establish the reliability of fetal amniocyte Rhesus D (RhD) genotyping using fluorescence duplex polymerase chain reaction (PCR) and 2. to assess the potential clinical impact on management of alloimmunised pregnancies.

DESIGN

Multicentre observational study.

SETTING

Four departments of obstetrics and gynaecology in Germany.

METHODS

Fourty-four amniotic fluid samples were obtained by amniocentesis from a retrospective group of 27 RhD alloimmunised pregnancies and 15 samples from 14 women treated prospectively. Two RhD gene specific fragments (exon 7 and 10) were amplified using two separate fluorescence duplex PCR assays, and laser detected in an automated DNA sequence analyser.

RESULTS

Amplification of the Rh gene sequences was successful in all samples. PCR at the two RhD gene regions resulted in complete concordance. Genotyping correctly predicted the RhD status of all fetuses serotyped (n = 41). After intrauterine transfusions, PCR identified the RhD type of two fetuses more accurately than serotyping. Earlier knowledge of a negative RhD status would have rendered unnecessary 12 amniocenteses in four fetuses of the retrospective study group, and prevented further invasive testing in one fetus treated prospectively. In the latter group, women with a positive fetal RhD genotype underwent intensive prenatal care including serial invasive monitoring and intrauterine treatment.

CONCLUSIONS

Fetal RhD genotyping of amniocytes is a reliable technique with the potential to improve routine management of alloimmunised pregnant women.