title: Comparing outcomes and costs between contingent and combined first-trimester screening strategies for Down's syndrome.
abstract: OBJECTIVE
  To compare a contingent strategy with a combined strategy for prenatal detection of Down's syndrome (DS) in terms of cost, outcomes and safety.
  
  
  METHODS
  The contingent strategy was based on a simulation, removing measurement of the free beta subunit of human chorionic gonadotropin (free βhCG) and calculating the DS risk retrospectively in 32,371 pregnant women who had been screened with the combined strategy in the first trimester. In the contingent strategy, a risk between 1:31 and 1:1000 in the first trimester indicated further testing in the second trimester (alpha-fetoprotein, inhibin A, unconjugated oestriol and free βhCG). The cut-off risk values for the contingent and combined strategies in the first trimester were 1:30 and 1:250, respectively, and the cut-off risk value for integrated screening in the second trimester was 1:250. Costs were compared in terms of avoided DS births, and the ratio of loss of healthy fetuses following invasive procedures per avoided DS birth was calculated.
  
  
  RESULTS
  The combined strategy had sensitivity of 40/44 (90.9%) and a false-positive rate of 2.8%. Corresponding values for the contingent strategy were 39/44 (88.6%) and 1.3%, respectively. Only 11% of pregnant women required tests in the second trimester, and the approximate cost reduction for each avoided DS birth was 5000€. The ratio of lost healthy fetuses following invasive procedures per avoided DS birth improved by up to 0.65.
  
  
  CONCLUSIONS
  The contingent strategy has similar effectiveness to the combined strategy, but has lower costs and fewer invasive procedures.
authors.affiliation: Servicio de Análisis Clínicos, Hospital Universitario Son Espases, Palma, Mallorca, Spain. Electronic address: inmaculada.martin@ssib.es.
authors.forename: I
authors.initials: I
authors.lastname: Martín
authors.affiliation: Servicio de Obstetricia y Ginecología, Hospital Universitario Son Espases, Palma, Mallorca, Spain.
authors.forename: M J
authors.initials: MJ
authors.lastname: Gibert
authors.affiliation: Servicio de Bioquímica, Hospital Vall d'Hebrón, Barcelona, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Aulesa
authors.affiliation: Servicio de Análisis Clínicos Catlab, Barcelona, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Alsina
authors.affiliation: Servicio de Bioquímica, Hospital Clínic, Barcelona, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Casals
authors.affiliation: Servicio de Análisis Clínicos, Hospital Universitario Son Espases, Palma, Mallorca, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Bauça
mesh_terms: D000328:Adult; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D003365:Costs and Cost Analysis; D004314:Down Syndrome / Q000175:diagnosis*; D004964:Estriol / Q000097:blood; D005189:False Positive Reactions; D005260:Female; D005865:Gestational Age; D006801:Humans; D007265:Inhibins / Q000097:blood; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011262:Pregnancy Trimester, Second; D011296:Prenatal Diagnosis / Q000009:adverse effects / Q000191:economics* / Q000379:methods*; D012306:Risk; D018570:Risk Assessment; D000509:alpha-Fetoproteins / Q000032:analysis
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D000509:alpha-Fetoproteins; C422362:inhibin A; D007265:Inhibins; D004964:Estriol
keywords: Choriogonadotrophin; Cost; Down's syndrome; Outcomes; Prenatal screening