title: Effect of non-invasive prenatal testing as a contingent approach on the indications for invasive prenatal diagnosis and prenatal detection rate of Down's syndrome.
abstract: BACKGROUND
  In Hong Kong, universal combined first-trimester screening for Down's syndrome was started as a 'free service' in July 2010. Non-invasive prenatal testing was available as a self-financed item in August 2011. This study aimed to determine whether the introduction of non-invasive prenatal testing as a contingent approach influenced the indications for invasive prenatal diagnosis and the consequent prenatal detection of Down's syndrome.
  
  
  METHODS
  This historical cohort study was conducted at the Prenatal Diagnosis Clinic of Queen Elizabeth Hospital in Hong Kong. We compared the indications for invasive prenatal diagnosis and prenatal detection of Down's syndrome in singleton pregnancies 1 year before and 2 years following the availability of non-invasive prenatal testing as a contingent test after a positive aneuploidy test. All pregnant women who attended our hospital for counselling about universal Down's syndrome screening between August 2010 and July 2013 were recruited.
  
  
  RESULTS
  A total of 16 098 women were counselled. After the introduction of non-invasive prenatal testing, the invasive prenatal diagnosis rate for a positive aneuploidy screening reduced from 77.7% in 2010-11 to 68.8% in 2012-13. The new combined conventional plus non-invasive prenatal testing strategy was associated with a lower false-positive rate (6.9% in 2010-11 vs 5.2% in 2011-12 and 4.9% in 2012-13). There was no significant increase in invasive prenatal diagnosis for structural anomalies over the years. There was no significant trend in the overall prenatal detection rate of Down's syndrome (100% 1 year before vs 89.1% 2 years after introduction of non-invasive prenatal testing). Four (2.6%) of 156 women who underwent non-invasive prenatal testing for a screen-positive result had a high-risk result for trisomy 21, which was subsequently confirmed by invasive prenatal diagnosis. There were no false-negative cases.
  
  
  CONCLUSIONS
  The introduction of non-invasive prenatal testing as a contingent approach reduced the invasive prenatal diagnosis rate for a positive aneuploidy screening without affecting the invasive prenatal diagnosis rate for structural anomalies or the overall detection rate of fetal Down's syndrome.
authors.affiliation: Department of Obstetrics and Gynaecology, Queen Elizabeth Hospital, Jordan, Hong Kong.
authors.forename: K O
authors.initials: KO
authors.lastname: Kou
authors.affiliation: Department of Obstetrics and Gynaecology, Queen Elizabeth Hospital, Jordan, Hong Kong.
authors.forename: C F
authors.initials: CF
authors.lastname: Poon
authors.affiliation: Department of Obstetrics and Gynaecology, Queen Elizabeth Hospital, Jordan, Hong Kong.
authors.forename: S L
authors.initials: SL
authors.lastname: Kwok
authors.affiliation: Prenatal Diagnostic Laboratory, Tsan Yuk Hospital and Department of Obstetrics and Gynaecology, Queen Mary Hospital, Hong Kong.
authors.forename: K Yk
authors.initials: KY
authors.lastname: Chan
authors.affiliation: Prenatal Diagnostic Laboratory, Tsan Yuk Hospital and Department of Obstetrics and Gynaecology, Queen Mary Hospital, Hong Kong.
authors.forename: M Hy
authors.initials: MH
authors.lastname: Tang
authors.affiliation: Prenatal Diagnostic Laboratory, Tsan Yuk Hospital and Department of Obstetrics and Gynaecology, Queen Mary Hospital, Hong Kong.
authors.forename: A Sy
authors.initials: AS
authors.lastname: Kan
authors.affiliation: Department of Obstetrics and Gynaecology, Queen Elizabeth Hospital, Jordan, Hong Kong.
authors.forename: K Y
authors.initials: KY
authors.lastname: Leung
mesh_terms: D000328:Adult; D000782:Aneuploidy; D015415:Biomarkers / Q000097:blood*; D015331:Cohort Studies; D004314:Down Syndrome / Q000175:diagnosis* / Q000453:epidemiology*; D005189:False Positive Reactions; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008403:Mass Screening / Q000379:methods*; D008423:Maternal Age; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011296:Prenatal Diagnosis / Q000706:statistics & numerical data* / Q000639:trends
chemical_list: D015415:Biomarkers
keywords: Aneuploidy; Down syndrome; Prenatal diagnosis