title: Sequential testing for Down syndrome: the impact on estimated risk.
abstract: OBJECTIVE
  Our objective was to describe the utilization of sequential screening and evaluate the impact on estimated Down syndrome risk.
  
  
  METHODS
  We reviewed records of all those undergoing first-trimester screening over a 3-year period. All patients received first-trimester Down syndrome risk, and had options of invasive testing and sequential testing. We compared adjusted first-trimester Down syndrome risk with adjusted risk following sequential testing. Fisher's exact test and chi-square for trend were used for statistical comparison.
  
  
  RESULTS
  First-trimester screening was performed on 12,557 patients. The rate of sequential testing was 34.0%. In 13.1% of patients, sequential testing resulted in a higher risk compared with first-trimester risk, with a risk at least twice as high in 5.2%. The likelihood that sequential testing would increase risk progressively decreased as first-trimester risk declined, from 17.8% for those with first-trimester risk of >1 in 270 to 8.7% in those with first-trimester risk of <1 in 10,000 (p < .001). For those with first-trimester risk <1 in 2000, the likelihood that sequential testing would adjust risk to >1 in 270 was <1%.
  
  
  CONCLUSIONS
  Sequential testing lowers the Down syndrome risk in most cases and is more likely to do so with decreasing first-trimester risk.
authors.affiliation: Weill Medical College of Cornell University, Department of Obstetrics and Gynecology, New York, NY, USA. stchasen@med.cornell.edu
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Chasen
authors.forename: Shane
authors.initials: S
authors.lastname: Wasden
mesh_terms: D000328:Adult; D015415:Biomarkers; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D004314:Down Syndrome / Q000097:blood / Q000175:diagnosis* / Q000235:genetics; D005260:Female; D005817:Genetic Counseling; D005865:Gestational Age; D006801:Humans; D007621:Karyotyping; D008403:Mass Screening / Q000379:methods*; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000097:blood; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis; D011296:Prenatal Diagnosis / Q000379:methods*; D018570:Risk Assessment / Q000379:methods
chemical_list: D015415:Biomarkers; D018997:Chorionic Gonadotropin, beta Subunit, Human; C430889:PAPPA2 protein, human; D011266:Pregnancy-Associated Plasma Protein-A