title: First-trimester combined screening for trisomy 21 in a predominantly Chinese population.
abstract: OBJECTIVE
  To examine the effectiveness of first-trimester fetal trisomy 21 screening using a combination of maternal age, nuchal translucency thickness (NT) and maternal serum free beta-human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein-A (PAPP-A) levels in a predominantly Chinese population in Hong Kong.
  
  
  METHODS
  This was a prospective study over a 1.5-year period of 2990 women who underwent combined screening for trisomy 21 between 11+0 and 13+6 weeks of gestation in a university fetal medicine unit. NT was measured according to the criteria set by The Fetal Medicine Foundation (FMF), maternal serum free beta-hCG and PAPP-A levels were measured, and the risk of trisomy 21 was calculated using The FMF's algorithm. Fetal karyotyping was advised when the risk was 1 : 300 or above. All subjects were followed up for pregnancy and fetal outcome.
  
  
  RESULTS
  Of the 2990 women who underwent the screening program, 99% were Chinese. There were 57 twin pregnancies, giving a total of 3047 fetuses. Thirty-one percent of the women were 35 years old or above. One hundred and eighty-five (6.1%) fetuses were screen-positive; this included 14 cases of trisomy 21 and 17 cases of other chromosomal abnormalities. The positive predictive value was 16.7%. Among the 2862 screen-negative fetuses, only 18 (0.6%) cases had an unknown fetal outcome. There were no cases in which trisomy 21 was missed and the infant was liveborn.
  
  
  CONCLUSIONS
  First-trimester combined screening for fetal trisomy 21 is highly effective among Chinese subjects.
authors.affiliation: Department of Obstetrics and Gynecology, The Chinese University of Hong Kong, Hong Kong, China SAR.
authors.forename: T Y
authors.initials: TY
authors.lastname: Leung
authors.affiliation: Department of Obstetrics and Gynecology, The Chinese University of Hong Kong, Hong Kong, China SAR.
authors.forename: L W
authors.initials: LW
authors.lastname: Chan
authors.affiliation: Department of Obstetrics and Gynecology, The Chinese University of Hong Kong, Hong Kong, China SAR.
authors.forename: T N
authors.initials: TN
authors.lastname: Leung
authors.affiliation: Department of Obstetrics and Gynecology, The Chinese University of Hong Kong, Hong Kong, China SAR.
authors.forename: T Y
authors.initials: TY
authors.lastname: Fung
authors.affiliation: Department of Obstetrics and Gynecology, The Chinese University of Hong Kong, Hong Kong, China SAR.
authors.forename: D S
authors.initials: DS
authors.lastname: Sahota
authors.affiliation: Prenatal Screening Unit, Clinical Biochemistry Department, Harold Wood Hospital, Romford, Essex, UK.
authors.forename: K
authors.initials: K
authors.lastname: Spencer
authors.affiliation: Department of Obstetrics and Gynecology, The Chinese University of Hong Kong, Hong Kong, China SAR.
authors.forename: T K
authors.initials: TK
authors.lastname: Lau
mesh_terms: D000328:Adult; D044466:Asian People / Q000208:ethnology; D015415:Biomarkers / Q000097:blood; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D004314:Down Syndrome / Q000175:diagnosis* / Q000208:ethnology / Q000235:genetics; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis*; D011296:Prenatal Diagnosis / Q000379:methods*; D011446:Prospective Studies
chemical_list: D015415:Biomarkers; D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A