title: Stepwise sequential screening for fetal aneuploidy.
abstract: OBJECTIVE
  The purpose of this study was to evaluate stepwise sequential screening for fetal aneuploidy.
  
  
  METHODS
  Women who received first-trimester screening were also offered second-trimester tests with second-trimester risks that were based on both sets of markers. Screen-positive rates, use of second-trimester testing and invasive testing, sensitivity, and changes in risks were evaluated.
  
  
  RESULTS
  Of 1528 women who received first-trimester screening, 133 women (8.7%) had an indication for invasive testing that was based on first-trimester results alone; 1173 women (76.8%) received second-trimester tests, which reduced the net number of women with an indication for invasive testing to 105 (6.9%). In unaffected pregnancies, the addition of the second-trimester testing reduced the median Down syndrome risk from 1:2368 to 1:10,301. Six of 10 chromosome abnormalities (60%) were identified by first-trimester screening, and 9 of 10 chromosome abnormalities (90%) were identified by sequential screening.
  
  
  CONCLUSIONS
  Sequential screening can be introduced successfully into clinical practice, is effective, and can reduce the number of invasive tests that are performed.
authors.affiliation: Division of Human Genetics, Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT, USA.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Benn
authors.forename: Winston A
authors.initials: WA
authors.lastname: Campbell
authors.forename: Carolyn M
authors.initials: CM
authors.lastname: Zelop
authors.forename: Charles
authors.initials: C
authors.lastname: Ingardia
authors.forename: James F X
authors.initials: JF
authors.lastname: Egan
mesh_terms: D000328:Adult; D000782:Aneuploidy; D005260:Female; D005315:Fetal Diseases / Q000175:diagnosis* / Q000235:genetics*; D005820:Genetic Testing / Q000379:methods*; D006801:Humans; D011247:Pregnancy; D011296:Prenatal Diagnosis