title: Triple test for prenatal detection of Edwards syndrome (trisomy 18).
abstract: OBJECTIVE
  To demonstrate the limitation of complete reliance on computer generated interpretations and to highlight the need for understanding of pregnancy-related biochemistry when offering prenatal screening.
  
  
  METHODS
  Four cases of cytogenetically confirmed trisomy 18 pregnancies are presented. All four cases underwent prenatal screening (Triple Test-AFP, uE3, t beta-hCG) at midgestation and risk assessment by the alpha algorithm.
  
  
  RESULTS
  All four cases of trisomy 18 were assessed as being at low risk for DS and/or open NTD. Although marker levels were not consistent with either of these clinical situations, they were indicative of a compromised pregnancy. Circulating levels of trophoblast-derived antigens (uE3, t beta-hCG) were depressed (< or = 0.5 MoM) in all four cases. Further investigations (ultrasonography, amniocentesis) confirmed a trisomy 18 fetus.
  
  
  CONCLUSIONS
  Risk assessment by computer based algorithms relies on maternal factors and specific DS/NTD marker profiles. Aberrant marker profiles are not distinguished from normal. Therefore, it is essential that prenatal screening is offered only by those competent in pregnancy biochemistry and able to identify these abnormal situations.
authors.affiliation: Royal North Shore Hospital, St Leonards, Australia.
authors.forename: M J
authors.initials: MJ
authors.lastname: Sinosich
authors.forename: B
authors.initials: B
authors.lastname: Cameron
authors.forename: R D
authors.initials: RD
authors.lastname: Robertson
authors.forename: D M
authors.initials: DM
authors.lastname: Saunders
mesh_terms: D000328:Adult; D000465:Algorithms; D015415:Biomarkers; D002887:Chromosomes, Human, Pair 18; D003936:Diagnosis, Computer-Assisted; D005260:Female; D006801:Humans; D009436:Neural Tube Defects / Q000175:diagnosis; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D018570:Risk Assessment; D014314:Trisomy
chemical_list: D015415:Biomarkers