title: Cell-free DNA analysis for trisomy risk assessment in first-trimester twin pregnancies.
abstract: OBJECTIVE
  To examine the clinical implementation of chromosome-selective sequencing of cell-free DNA (cfDNA) in maternal blood and an algorithm that relies on the lower fetal fraction contribution of the 2 fetuses in the assessment of risk for trisomies in twin pregnancies.
  
  
  METHODS
  Risk for trisomies 21, 18 and 13 by cfDNA testing were estimated in stored plasma samples obtained at 11-13 weeks' gestation from 207 pregnancies with known outcome and prospectively in 68 twin pregnancies undergoing screening at 10-13 weeks.
  
  
  RESULTS
  Risk scores for trisomies were provided for 192 (92.8%) of stored plasma and for 63 (92.6%) of the prospective cases. In the retrospective study, 10 of 11 trisomic pregnancies were correctly identified with no false positive results. In the prospective study, 3 trisomic pregnancies were correctly identified with no false positive results. The median of the lower fetal fraction in the prospective study of twins was 7.4% (IQR range 5.9-10.0%), which was lower than in our previous study in singletons (median 10.0%, IQR 7.8-13.0%).
  
  
  CONCLUSIONS
  cfDNA testing in twins is feasible but the reporting rate of results is lower than in singletons due to a lower fetal fraction.
authors.affiliation: Harris Birthright Research Centre of Fetal Medicine, King's College Hospital, London, UK.
authors.forename: Maria
authors.initials: M
authors.lastname: del Mar Gil
authors.forename: Maria Soledad
authors.initials: MS
authors.lastname: Quezada
authors.forename: Barbara
authors.initials: B
authors.lastname: Bregant
authors.forename: Argyro
authors.initials: A
authors.lastname: Syngelaki
authors.forename: Kypros H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D000328:Adult; D002474:Cell-Free System / Q000502:physiology; D004247:DNA / Q000235:genetics*; D005260:Female; D006801:Humans; D062145:Maternal Serum Screening Tests / Q000379:methods*; D008875:Middle Aged; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000235:genetics*; D059285:Pregnancy, Twin / Q000235:genetics*; D011296:Prenatal Diagnosis / Q000379:methods; D011446:Prospective Studies; D012189:Retrospective Studies; D018570:Risk Assessment; D014314:Trisomy / Q000235:genetics*
chemical_list: D004247:DNA