title: Microfluidics digital PCR reveals a higher than expected fraction of fetal DNA in maternal plasma.
abstract: BACKGROUND
  The precise measurement of cell-free fetal DNA in maternal plasma facilitates noninvasive prenatal diagnosis of fetal chromosomal aneuploidies and other applications. We tested the hypothesis that microfluidics digital PCR, in which individual fetal-DNA molecules are counted, could enhance the precision of measuring circulating fetal DNA.
  
  
  METHODS
  We first determined whether microfluidics digital PCR, real-time PCR, and mass spectrometry produced different estimates of male-DNA concentrations in artificial mixtures of male and female DNA. We then focused on comparing the imprecision of microfluidics digital PCR with that of a well-established nondigital PCR assay for measuring male fetal DNA in maternal plasma.
  
  
  RESULTS
  Of the tested platforms, microfluidics digital PCR demonstrated the least quantitative bias for measuring the fractional concentration of male DNA. This assay had a lower imprecision and higher clinical sensitivity compared with nondigital real-time PCR. With the ZFY/ZFX assay on the microfluidics digital PCR platform, the median fractional concentration of fetal DNA in maternal plasma was > or =2 times higher for all 3 trimesters of pregnancy than previously reported.
  
  
  CONCLUSIONS
  Microfluidics digital PCR represents an improvement over previous methods for quantifying fetal DNA in maternal plasma, enabling diagnostic and research applications requiring precise quantification. This approach may also impact other diagnostic applications of plasma nucleic acids, e.g., in oncology and transplantation.
authors.affiliation: Centre for Research into Circulating Fetal Nucleic Acids, Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
authors.forename: Fiona M F
authors.initials: FM
authors.lastname: Lun
authors.forename: Rossa W K
authors.initials: RW
authors.lastname: Chiu
authors.forename: K C Allen
authors.initials: KC
authors.lastname: Chan
authors.forename: Tak Yeung
authors.initials: TY
authors.lastname: Leung
authors.forename: Tze Kin
authors.initials: TK
authors.lastname: Lau
authors.forename: Y M Dennis
authors.initials: YM
authors.lastname: Lo
mesh_terms: D004247:DNA / Q000097:blood*; D005260:Female; D006801:Humans; D008431:Maternal-Fetal Exchange; D044085:Microfluidics / Q000295:instrumentation*; D016133:Polymerase Chain Reaction / Q000379:methods*; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D004247:DNA