title: Quantification of free fetal DNA in multiple pregnancies and relationship with chorionicity.
abstract: OBJECTIVE
  Free fetal DNA (ffDNA) in the maternal plasma appears to originate mainly from the trophoblast. We tested the hypothesis that ffDNA concentration is increased in multiple pregnancies where trophoblastic mass has been shown to be increased.
  
  
  METHODS
  Quantitative real-time PCR was used to measure the plasma concentration of DYS14 in singleton and twin pregnancies with one or two male fetuses. Royston and Wright's regression method was used to relate ffDNA to gestational age in singleton controls; z-scores were calculated for the multiple pregnancy subgroups.
  
  
  RESULTS
  Fifty-five singleton and 65 twin pregnancies (36 with one and 29 with two male fetuses) were analysed. There was significantly higher ffDNA concentration in twin pregnancies with two male fetuses compared with pregnancies with one male fetus. In cases with two male fetuses, there was no statistically significant difference between monochorionic and dichorionic pregnancies.
  
  
  CONCLUSIONS
  There is higher ffDNA concentration in multiple pregnancies, and this must be taken into account for future quantitative ffDNA applications.
authors.affiliation: Fetal Medicine Unit, St Michael's Hospital, University Hospitals Bristol NHS Foundation Trust, Bristol, UK. georgeattilakos@doctors.org.uk
authors.forename: George
authors.initials: G
authors.lastname: Attilakos
authors.forename: Deborah G
authors.initials: DG
authors.lastname: Maddocks
authors.forename: Teresa
authors.initials: T
authors.lastname: Davies
authors.forename: Linda P
authors.initials: LP
authors.lastname: Hunt
authors.forename: Neil D
authors.initials: ND
authors.lastname: Avent
authors.forename: Peter W
authors.initials: PW
authors.lastname: Soothill
authors.forename: Simon R
authors.initials: SR
authors.lastname: Grant
mesh_terms: D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000097:blood; D018797:Cell Cycle Proteins / Q000097:blood / Q000235:genetics; D002823:Chorion / Q000033:anatomy & histology* / Q000378:metabolism; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D041322:Chromosomes, Human, Y / Q000235:genetics; D004247:DNA / Q000097:blood*; D005260:Female; D005333:Fetus / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D059285:Pregnancy, Twin / Q000097:blood*; D011296:Prenatal Diagnosis / Q000379:methods*; D014427:Twins; D055815:Young Adult
chemical_list: D015415:Biomarkers; D018797:Cell Cycle Proteins; D018997:Chorionic Gonadotropin, beta Subunit, Human; C497749:TSPY1 protein, human; D004247:DNA