title: Medians and correction factors for biochemical and ultrasound markers in Chinese women undergoing first-trimester screening for trisomy 21.
abstract: OBJECTIVE
  To establish normative values and distribution parameters of first-trimester maternal serum free beta-human chorionic gonadotropin (beta-hCG), pregnancy-associated plasma protein-A (PAPP-A) and fetal nuchal translucency (NT) thickness in Chinese women and to examine the effects of covariates on their levels.
  
  
  METHODS
  Maternal serum free beta-hCG, PAPP-A and fetal NT were measured in 9762 women presenting for first-trimester combined screening for Down syndrome at 11 to 14 weeks of gestation. Individuals' markers were converted to multiples of the median (MoM) using expected medians estimated by performing a weighted regression analysis. Multivariate regression analysis was performed to assess the influence of maternal weight, parity, ethnicity, chorionicity in twin pregnancies, smoking, insulin-dependent diabetes and mode of conception on individual marker MoM levels.
  
  
  RESULTS
  Both free beta-hCG and PAPP-A median values demonstrated an exponential relationship with gestational age in days. Multivariate regression analysis indicated that free beta-hCG MoM was statistically significantly dependent on maternal weight (P < 0.0001) and chorionicity in twin pregnancy (both monochorionic and dichorionic P < 0.0001), that PAPP-A MoM was dependent on maternal weight (P < 0.0001), parity (P < 0.0001), chorionicity in twin pregnancy (both monochorionic and dichorionic P < 0.0001) and mode of conception (P = 0.002), and that fetal NT-MoM was dependent on maternal weight (P = 0.0006) and mode of conception (P = 0.012).
  
  
  CONCLUSIONS
  Normative values have been generated to allow conversion of NT, free beta-hCG and PAPP-A to their MoM equivalents and correction factors have been determined to adjust for maternal and pregnancy characteristics for use in ethnic Chinese women undergoing first-trimester screening for aneuploidy.
authors.affiliation: Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong, The Prince of Wales Hospital, Shatin, Hong Kong SAR, China. daljit@cuhk.edu.hk
authors.forename: D S
authors.initials: DS
authors.lastname: Sahota
authors.forename: T Y
authors.initials: TY
authors.lastname: Leung
authors.forename: T Y
authors.initials: TY
authors.lastname: Fung
authors.forename: L W
authors.initials: LW
authors.lastname: Chan
authors.forename: L W
authors.initials: LW
authors.lastname: Law
authors.forename: T K
authors.initials: TK
authors.lastname: Lau
mesh_terms: D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000097:blood; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D018568:Crown-Rump Length; D004314:Down Syndrome / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000208:ethnology; D004812:Epidemiologic Methods; D005260:Female; D005315:Fetal Diseases / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000208:ethnology; D005865:Gestational Age; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008297:Male; D008423:Maternal Age; D008875:Middle Aged; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011266:Pregnancy-Associated Plasma Protein-A / Q000378:metabolism; D011296:Prenatal Diagnosis / Q000379:methods*; D012016:Reference Values; D055815:Young Adult
chemical_list: D015415:Biomarkers; D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A