title: First trimester combined test for Down syndrome screening in unselected pregnancies - a report of a 13-year experience.
abstract: OBJECTIVE
  To analyze the performance of the first trimester Down syndrome screening in a single medical center in Northern Taiwan.
  
  
  METHODS
  From April 1999 to June 2012, a total of 25,104 pregnant women at gestational age of 10 weeks to 13 weeks 6 days received first trimester "combined test" for Down syndrome screening. The test combines the ultrasound scan of nuchal translucency thickness and maternal biochemical serum levels of pregnancy-associated plasma protein A (PAPP-A) and free beta-human chorionic gonadotropin (β-hCG). A positive screen was defined as an estimated Down syndrome risk ≥ 1/270, and either chorionic villous sampling or amniocentesis was performed for fetal chromosomal analyses.
  
  
  RESULTS
  Seventy-eight of the 25,104 pregnancies were proven to have fetal chromosome anomalies. The detection rates for trisomy 21, trisomy 18, Turner syndrome, and other chromosome anomalies were 87.5% (21/24), 69.2% (9/13), 81.8% (9/11), and 60% (18/30), respectively, with a false positive rate (FPR) of 5.4% (1353/25,026). Further evaluation of the detection rates for trisomy 21, by gestational age at 11, 12, and 13 weeks, were 92.3%, 87.5%, and 66.7%, respectively.
  
  
  CONCLUSIONS
  The first trimester combined test is an effective screening tool for Down syndrome detection with an acceptable low false positive rate. The best timing of screening will be between 11 and 12 weeks' gestation.
authors.affiliation: Department of Obstetrics and Gynecology, Cathay General Hospital, Taipei, Taiwan.
authors.forename: Fa-Kung
authors.initials: FK
authors.lastname: Lee
authors.affiliation: Department of Obstetrics and Gynecology, Cathay General Hospital, Taipei, Taiwan.
authors.forename: Li-Ching
authors.initials: LC
authors.lastname: Chen
authors.affiliation: Department of Obstetrics and Gynecology, Cathay General Hospital, Taipei, Taiwan; School of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Mei-Leng
authors.initials: ML
authors.lastname: Cheong
authors.affiliation: Department of Obstetrics and Gynecology, Cathay General Hospital, Hsinchu Branch, Hsinchu, Taiwan.
authors.forename: Ching-Yu
authors.initials: CY
authors.lastname: Chou
authors.affiliation: Department of Obstetrics and Gynecology, Cathay General Hospital, Taipei, Taiwan; School of Medicine, Fu Jen Catholic University, Taipei, Taiwan; School of Medicine, Taipei Medical University, Taipei, Taiwan. Electronic address: mstsai@cgh.org.tw.
authors.forename: Ming-Song
authors.initials: MS
authors.lastname: Tsai
mesh_terms: D000328:Adult; D002887:Chromosomes, Human, Pair 18; D004314:Down Syndrome / Q000097:blood* / Q000000981:diagnostic imaging*; D005189:False Positive Reactions; D005260:Female; D005820:Genetic Testing; D006801:Humans; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000097:blood*; D011266:Pregnancy-Associated Plasma Protein-A / Q000378:metabolism*; D013624:Taiwan; D014314:Trisomy / Q000175:diagnosis; D000073842:Trisomy 18 Syndrome; D014424:Turner Syndrome / Q000175:diagnosis
chemical_list: D011266:Pregnancy-Associated Plasma Protein-A
keywords: Down syndrome screening; combined test; first trimester; prenatal diagnosis