title: Fetal RHD genotyping in maternal plasma at 11-13 weeks of gestation.
abstract: OBJECTIVE
  To examine the feasibility of fetal RHD genotyping at 11-13 weeks' gestation from analysis of circulating cell-free fetal DNA (ccffDNA) in the plasma of RhD negative pregnant women using a high-throughput robotic technique.
  
  
  METHODS
  Stored plasma (0.5 ml) from 591 RhD negative women was used for extraction of ccffDNA by a robotic technique. Real-time quantitative polymerase chain reaction (PCR) with probes for exons 5 and 7 of the RHD gene was then used to determine the fetal RHD genotype, which was compared to the neonatal RhD phenotype.
  
  
  RESULTS
  In total there were 502 (85.7%) cases with a conclusive result and 84 (14.3%) with an inconclusive result. The prenatal test predicted that the fetus was RhD positive in 332 cases and in all of these the prediction was correct, giving a positive predictive value of 100% (95% CI 96.8-100). The test predicted that the fetus was RhD negative in 170 cases and in 164 of these the prediction was correct, giving a negative predictive value for RhD positive fetuses of 96.5% (95% CI 93.7-99.2).
  
  
  CONCLUSIONS
  The findings demonstrate the feasibility and accuracy of non-invasive fetal RHD genotyping at 11-13 weeks with a high-throughput technique.
authors.affiliation: Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
authors.forename: Ranjit
authors.initials: R
authors.lastname: Akolekar
authors.forename: Kirstin
authors.initials: K
authors.lastname: Finning
authors.forename: Ramesh
authors.initials: R
authors.lastname: Kuppusamy
authors.forename: Geoff
authors.initials: G
authors.lastname: Daniels
authors.forename: Kypros H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D004247:DNA / Q000097:blood*; D005240:Feasibility Studies; D005260:Female; D005312:Fetal Blood / Q000276:immunology*; D005838:Genotype; D005865:Gestational Age; D006801:Humans; D010641:Phenotype; D011247:Pregnancy; D012204:Rh-Hr Blood-Group System / Q000235:genetics*; D012680:Sensitivity and Specificity
chemical_list: D012204:Rh-Hr Blood-Group System; D004247:DNA