title: Down syndrome screening in assisted conception twins: an iatrogenic medical challenge.
abstract: OBJECTIVE
  The objective of this study was to provide a critical analysis of the impact of assisted conception on prenatal screening for Down syndrome (DS) in twin pregnancies and the value of various screening modalities for early detection of anomalies.
  
  
  METHODS
  The literature was searched using PubMed and the Cochrane Library focusing on prenatal screening and antenatal care of assisted-conception twin pregnancies.
  
  
  RESULTS
  Serum screening alone is of limited value in detecting aneuploid twins, because the unaffected cotwin can "mask" the abnormal serum results of an affected one. In addition, this test can designate the pregnancy as at high risk but not identify the affected fetus. Nuchal translucency (NT) screening is the best available modality and a highly effective screening method for twin pregnancies. Among twins, NT alone has a 69% DS detection rate, first-trimester combined NT and serum biochemistry has a 72% DS detection rate, and an integrated screen will have an 80% DS detection rate at a 5% FPR. The data in the literature concerning the effect of assisted conception on maternal serum screening markers in twin pregnancies are scarce.
  
  
  CONCLUSIONS
  Down syndrome screening in assisted-conception twins presents clinical and technical challenges. Therefore, assisted-conception twins need close monitoring from conception to delivery, by a practitioner familiar with the available screening modalities and their relative accuracy.
authors.affiliation: Senior Lecturer, Infertility Clinic.
authors.forename: Ido
authors.initials: I
authors.lastname: Ben-Ami
authors.forename: Ron
authors.initials: R
authors.lastname: Maymon
authors.forename: Ran
authors.initials: R
authors.lastname: Svirsky
authors.forename: Howard
authors.initials: H
authors.lastname: Cuckle
authors.forename: Eric
authors.initials: E
authors.lastname: Jauniaux
mesh_terms: D004200:Diseases in Twins / Q000175:diagnosis*; D004314:Down Syndrome / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007049:Iatrogenic Disease; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011264:Pregnancy Trimesters; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis; D011296:Prenatal Diagnosis / Q000379:methods*; D027724:Reproductive Techniques, Assisted; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
chemical_list: D011266:Pregnancy-Associated Plasma Protein-A