title: Improved performance of first-trimester combined screening for trisomy 21 with the double test taken before a gestational age of 10 weeks.
abstract: OBJECTIVE
  To evaluate if there is a performance difference in the combined screening for trisomy 21 between the double tests performed before and after 10 + 0 weeks of gestation.
  
  
  METHODS
  The study included all 97 trisomy 21 cases from January 2004 to December 2007, in a screening program where the double test was measured in week 8 + 0 to 13 + 6 and the nuchal translucency in week 11 + 3 to 13 + 6.
  
  
  RESULTS
  As many as 87 of the 97 cases were diagnosed in the screening program (detection rate = 90%). Among the 53 cases having the double test taken before 10 + 0 weeks, no cases were missed [detection rate (DR) = 100%, CI = 0.94-1.00] and among the 44 having the double test taken after 10 + 0 weeks, 10 cases were missed (DR = 77%, CI = 0.65-0.90). This difference in DR was highly significant (P = 0.0009). No difference was observed between false positive rates or median maternal age of the two groups.
  
  
  CONCLUSIONS
  A significantly higher DR was obtained when the double test was taken early in pregnancy (<10 + 0 weeks), than when it was taken later (>or=10 + 0 weeks). The results could not be explained by a difference in either the false positive rate or the maternal age between the two groups.
authors.affiliation: Department of Obstetrics and Gynecology, Aarhus University Hospital, Skejby, Aarhus, Denmark. ida.kirkegaard@ki.au.dk
authors.forename: Ida
authors.initials: I
authors.lastname: Kirkegaard
authors.forename: Olav Bjørn
authors.initials: OB
authors.lastname: Petersen
authors.forename: Niels
authors.initials: N
authors.lastname: Uldbjerg
authors.forename: Niels
authors.initials: N
authors.lastname: Tørring
mesh_terms: D000328:Adult; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D004314:Down Syndrome / Q000175:diagnosis*; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D005865:Gestational Age; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis*; D016216:Ultrasonography, Prenatal; D055815:Young Adult
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A