title: Combined test + inhibin A at week 13 in contingent sequential testing: an interesting alternative for first-trimester prenatal screening for Down syndrome.
abstract: OBJECTIVE
  To analyze various possibilities of using dimeric inhibin A (DIA) as a first-trimester marker, during week 13, for diverse sequential strategies together with the combined test (CT) [which uses pregnancy-associated plasma protein A, free beta-human chorionic gonadotrophin and nuchal translucency].
  
  
  METHODS
  We analyzed three sequential strategies (nondisclosure, stepwise and contingent) for measuring DIA in week 13. Multivariate Gaussian modelling was used to estimate second-trimester, false-positive and detection rates. Model parameters were taken from the Serum, Urine and Ultrasound Screening Study (SURUSS) assay.
  
  
  RESULTS
  The three sequential strategies provided high and comparable levels of effectiveness, with false-positive rate for fixed detection rate of 85% and detection rate for fixed false-positive rate of 5% values of about 91 and 2%, respectively. The contingent strategy (with two CT risk cutoffs, of 1 in 50 and 1 in 2000) produced a screening-positive rate of 0.8% with CT, while only 23% of the women needed subsequent DIA measurement.
  
  
  CONCLUSIONS
  First-trimester sequential screening using CT together with DIA measurement in week 13 is capable of producing results that are comparable with those of the integrated test, with the additional advantage that the final result is obtained earlier. It is recommended that this strategy be evaluated in large-scale prospective studies.
authors.affiliation: Spanish Gynaecology and Obstetrics Society, Spain. ramoscor@arrakis.es
authors.forename: D J
authors.initials: DJ
authors.lastname: Ramos-Corpas
authors.forename: J C
authors.initials: JC
authors.lastname: Santiago
mesh_terms: D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D004314:Down Syndrome / Q000175:diagnosis*; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D005865:Gestational Age; D006801:Humans; D007265:Inhibins / Q000097:blood*; D016013:Likelihood Functions; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis; D011296:Prenatal Diagnosis / Q000379:methods*; D012189:Retrospective Studies
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; C422362:inhibin A; D007265:Inhibins; D011266:Pregnancy-Associated Plasma Protein-A