title: Replacing the combined test by cell-free DNA testing in screening for trisomies 21, 18 and 13: impact on the diagnosis of other chromosomal abnormalities.
abstract: OBJECTIVE
  To estimate the proportion of other chromosomal abnormalities that could be missed if combined testing was replaced by cell-free (cf) DNA testing as the method of screening for trisomies 21, 18 and 13.
  
  
  METHODS
  The prevalence of trisomies 21, 18 or 13, sex chromosome aneuploidies, triploidy and other chromosomal abnormalities was examined in pregnancies undergoing first-trimester combined screening and chorionic villus sampling (CVS).
  
  
  RESULTS
  In 1,831 clinically significant chromosomal abnormalities in pregnancies with combined risk for trisomies 21, 18 and 13≥1:100, the contribution of trisomies 21, 18 or 13, sex chromosome aneuploidies, triploidy and other chromosomal abnormalities at high risk of adverse outcome was 82.9, 8.2, 3.9 and 5.0%, respectively. Combined screening followed by CVS for risk≥1:10 and cfDNA testing for risk 1:11-1:2,500 could detect 97% of trisomy 21 and 98% of trisomies 18 and 13. Additionally, 86% of monosomy X, half of 47,XXY, 47,XYY or 47,XXX, half of other chromosomal abnormalities and one third of triploidies, which are currently detected by combined screening and CVS for risk≥1:100, could be detected.
  
  
  CONCLUSIONS
  Screening by cfDNA testing, contingent on results of combined testing, improves detection of trisomies, but misses a few of the other chromosomal abnormalities detected by screening with the combined test.
authors: Harris Birthright Research Centre of Fetal Medicine, King's College Hospital, London, UK.
authors: Argyro
authors: A
authors: Syngelaki
authors: Eugene
authors: E
authors: Pergament
authors: Tessa
authors: T
authors: Homfray
authors: Ranjit
authors: R
authors: Akolekar
authors: Kypros H
authors: KH
authors: Nicolaides
mesh_terms: D000328:Adult; D002474:Cell-Free System / Q000502:physiology; D002869:Chromosome Aberrations / Q000196:embryology*; D025063:Chromosome Disorders / Q000175:diagnosis / Q000235:genetics*; D002882:Chromosomes, Human, Pair 13 / Q000235:genetics; D002887:Chromosomes, Human, Pair 18 / Q000235:genetics; D004247:DNA / Q000235:genetics*; D004314:Down Syndrome / Q000175:diagnosis / Q000235:genetics*; D005260:Female; D006801:Humans; D007621:Karyotyping / Q000379:methods* / Q000592:standards; D011247:Pregnancy; D014314:Trisomy / Q000175:diagnosis / Q000235:genetics*; D000073839:Trisomy 13 Syndrome; D000073842:Trisomy 18 Syndrome
chemical_list: D004247:DNA