title: Second-trimester Down syndrome maternal serum marker screening: a prospective study of 11 040 twin pregnancies.
abstract: OBJECTIVE
  To analyze the value of Down syndrome (DS) second-trimester maternal serum screening in large series of twin pregnancies.
  
  
  METHODS
  Prospective study of second-trimester maternal serum markers [alpha fetoprotein (AFP) and free beta-human chorionic gonadotrophin (beta-hCG)] in 11,040 twin pregnancies, 27 of which were trisomy 21-affected. Comparison with 64,815 singleton pregnancies, of which 86 were trisomy 21-affected. Markers were expressed in multiple of median (MoM) corrected by a previously defined coefficient (2.1 for AFP and 2.07 or 2.16 for free beta-hCG, dichorionic or monochorionic, respectively).
  
  
  RESULTS
  Trisomy 21 frequency was 1/649 for twins and 1/754 in singletons (NS). Mean detection rate was 63% (71% when both twins were affected and 60% when one was affected), versus 74.4% in singletons. False-positive rates were 10.8% in twins versus 10.3% in singletons (NS). No significant differences in MoM AFP and free beta-hCG values were noted between twins and singletons (0.92 and 0.78 for AFP and 1.54 and 2.68 for free beta-hCG, respectively).
  
  
  CONCLUSIONS
  Our study demonstrates that second-trimester DS maternal serum marker screening can be performed in twin pregnancies.
authors.affiliation: Biochimie-Hormonologie, Hôpital Robert Debré, AP-HP, Paris, France.
authors.forename: Aurélie
authors.initials: A
authors.lastname: Garchet-Beaudron
authors.forename: Sophie
authors.initials: S
authors.lastname: Dreux
authors.forename: Nathalie
authors.initials: N
authors.lastname: Leporrier
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Oury
authors.forename: Françoise
authors.initials: F
authors.lastname: Muller
mesh_terms: D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000097:blood*; D004200:Diseases in Twins / Q000175:diagnosis; D004314:Down Syndrome / Q000175:diagnosis* / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D009035:Mothers; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000097:blood*; D011272:Pregnancy, Multiple / Q000097:blood; D011296:Prenatal Diagnosis / Q000379:methods*; D011446:Prospective Studies; D014427:Twins
chemical_list: D015415:Biomarkers