title: First-trimester screening for down syndrome with serum sampling at different gestational ages: the effect on screening performance.
abstract: BACKGROUND
  The objective of this study was to evaluate the performance of first-trimester Down syndrome (DS) screening with serum sampling at different weeks of gestation.
  
  
  METHODS
  We studied 35,431 singleton pregnancies (2005-2011), including 145 DS cases. Screening performance was determined in different maternal age groups with serum sampling between weeks 9 + 0 and 13 + 6.
  
  
  RESULTS
  No significant differences were found between the detection rates at different gestational weeks. The false-positive rate (FPR) in week 9 (6%) was comparable to the FPR in week 10 (6.5%; p = 0.214), whereas it was significantly lower compared to weeks 11 (7.2%; p = 0.007), 12 (7.4%; p = 0.003) and 13 (8.5%; p < 0.001). The odds of receiving a false-positive result was significantly increased with serum sampling in week 11 (OR 1.32, 95% CI 1.08-1.63; p = 0.008) for women ≥36 years and from week 12 onwards (OR 1.28, 95% CI 1.01-1.61; p = 0.04) for women <36 years. There were no differences in mean log10 multiple of the median values of pregnancy-associated plasma protein-A, free β-human chorionic gonadotrophin or nuchal translucency between both age groups, nor in mean maternal age between the different gestational weeks in either age group.
  
  
  CONCLUSIONS
  Early serum sampling (<11 weeks) resulted in higher screening performance. The impact of the increase in the FPR was highest in women ≥36 years.
authors.affiliation: Department of Obstetrics and Gynaecology, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Melanie A J
authors.initials: MA
authors.lastname: Engels
authors.forename: Jos W R
authors.initials: JW
authors.lastname: Twisk
authors.forename: Marinus A
authors.initials: MA
authors.lastname: Blankenstein
authors.forename: John M G
authors.initials: JM
authors.lastname: van Vugt
mesh_terms: D004314:Down Syndrome / Q000175:diagnosis* / Q000235:genetics; D005260:Female; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011296:Prenatal Diagnosis / Q000379:methods*; D012044:Regression Analysis; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013997:Time Factors