title: First trimester screening cut-offs for noninvasive prenatal testing as a contingent screen: Balancing detection and screen-positive rates for trisomy 21.
abstract: OBJECTIVE
  To provide data on how screen-positive and detection rates of first trimester prenatal screening for fetal Down syndrome vary with changes in the risk cut-off and maternal age to inform contingency criteria for publicly funded noninvasive prenatal testing.
  
  
  METHODS
  First trimester screening and diagnostic data were collected for all women attending for first trimester fetal aneuploidy screening in Western Australia between 2005 and 2009. Prenatal screening and diagnostic data were linked to pregnancy outcomes, including data from the Midwives' Notification System and the Western Australian Registry of Developmental Anomalies. The prevalence of Down syndrome and performance of screening by risk cut-off and/or for women >35 years were analysed.
  
  
  RESULTS
  The current screening risk cut-off of 1:300 has screen-positive and detection rates of 3.5% and 82%. The screen-positive rate increases by 0.7-0.8% for each 100 point change in risk, up to 19.2% at 1:2500 (96% detection rate). Including all women >35 years as screen positive would increase the screen-positive rate and detection rates to 30.2% and 97.2%.
  
  
  CONCLUSIONS
  Variation in screening risk cut-off and the use of maternal age to assess eligibility for noninvasive testing could significantly impact the demand for, and cost of, the test. A contingent first trimester screening approach for risk assessment is superior to the use of a combination of screening and maternal age alone. These data will inform decisions regarding the criteria used to determine eligibility for publicly funded noninvasive prenatal testing.
authors.affiliation: Health Policy and Management, School of Public Health, Faculty of Health Sciences, Curtin University, Perth, Western Australia, Australia.
authors.forename: Susannah
authors.initials: S
authors.lastname: Maxwell
authors.affiliation: Institute for Immunology and Infectious Diseases, Murdoch University, Perth, Western Australia, Australia.
authors.forename: Ian
authors.initials: I
authors.lastname: James
authors.affiliation: School of Women's and Infants' Health, The University of Western Australia, Perth, Western Australia, Australia.
authors.forename: Jan E
authors.identifier: http://orcid.org/0000-0003-3928-3290
authors.initials: JE
authors.lastname: Dickinson
authors.affiliation: Health Policy and Management, School of Public Health, Faculty of Health Sciences, Curtin University, Perth, Western Australia, Australia.|School of Women's and Infants' Health, The University of Western Australia, Perth, Western Australia, Australia.|PathWest Laboratory Medicine, Princess Margaret Hospital, Perth, Western Australia, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: O'Leary
mesh_terms: D000328:Adult; D000465:Algorithms; D000066491:Clinical Decision-Making / Q000379:methods*; D004314:Down Syndrome / Q000175:diagnosis* / Q000191:economics / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D017048:Health Care Costs; D006291:Health Policy; D006801:Humans; D008423:Maternal Age; D062145:Maternal Serum Screening Tests / Q000191:economics / Q000379:methods / Q000592:standards; D018803:Models, Economic; D009313:National Health Programs / Q000191:economics; D011237:Predictive Value of Tests; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D018570:Risk Assessment; D016216:Ultrasonography, Prenatal / Q000191:economics / Q000379:methods / Q000592:standards; D014904:Western Australia / Q000453:epidemiology
keywords: first trimester screening; noninvasive prenatal testing; policy; prenatal screening