title: Fetal fraction in maternal plasma cell-free DNA at 11-13 weeks' gestation: effect of maternal and fetal factors.
abstract: OBJECTIVE
  It was the aim of this study to examine the possible effects of maternal and fetal characteristics on the fetal fraction in maternal plasma cell-free DNA (cfDNA) at 11-13 weeks' gestation.
  
  
  METHODS
  In a nested case-control study, cfDNA was extracted from maternal plasma obtained before chorionic villous sampling from 300 euploid, 50 trisomy 21 and 50 trisomy 18 pregnancies at 11-13 weeks' gestation. Chromosome-selective sequencing of maternal cfDNA non-polymorphic and polymorphic loci, where fetal alleles differ from maternal alleles, was used to determine the proportion of DNA which is of fetal origin. Multivariate regression analysis was used to determine which of the factors amongst maternal weight, racial origin, smoking status, plasma storage time, serum pregnancy-associated plasma protein (PAPP)-A and free β-subunit of human chorionic gonadotropin (β-hCG), fetal crown-rump length, nuchal translucency thickness, gender and karyotype were significant predictors of the fetal fraction.
  
  
  RESULTS
  Significant independent prediction of fetal fraction was provided by maternal weight, serum PAPP-A and serum free β-hCG multiples of the median, but not by other maternal characteristics, fetal karyotype, crown-rump length or nuchal translucency thickness. Fetal fraction increased with serum metabolite levels and decreased with maternal weight.
  
  
  CONCLUSIONS
  The fetal fraction in maternal plasma cfDNA increases with serum PAPP-A and free β-hCG and decreases with maternal weight.
authors.affiliation: Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
authors.forename: Ghalia
authors.initials: G
authors.lastname: Ashoor
authors.forename: Leona
authors.initials: L
authors.lastname: Poon
authors.forename: Argyro
authors.initials: A
authors.lastname: Syngelaki
authors.forename: Beatrice
authors.initials: B
authors.lastname: Mosimann
authors.forename: Kypros H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D001835:Body Weight; D016022:Case-Control Studies; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D015193:Chorionic Villi Sampling; D002887:Chromosomes, Human, Pair 18; D004247:DNA / Q000097:blood*; D004314:Down Syndrome / Q000097:blood / Q000235:genetics; D005260:Female; D005333:Fetus; D005865:Gestational Age; D006801:Humans; D007621:Karyotyping; D011247:Pregnancy; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis*; D011296:Prenatal Diagnosis / Q000379:methods*; D014314:Trisomy / Q000175:diagnosis / Q000235:genetics
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D004247:DNA; D011266:Pregnancy-Associated Plasma Protein-A