title: Maternal serum unconjugated oestriol and human chorionic gonadotrophin levels in twin pregnancies: implications for screening for Down's syndrome.
abstract: OBJECTIVE
  To investigate maternal serum unconjugated oestriol (uE3) and human chorionic gonadotrophin (hCG) levels in twin pregnancies and to consider the implications of the results for antenatal screening for Down's syndrome.
  
  
  METHODS
  Measurement of maternal serum uE3 and hCG levels from 15-22 weeks of gestation in twin and singleton pregnancies. Previously available maternal serum alpha-fetoprotein (AFP) levels were also presented.
  
  
  METHODS
  Stored serum samples collected from women receiving routine antenatal care in Oxford were used.
  
  
  METHODS
  200 women with a twin pregnancy and, for each, three singleton control pregnancies matched for gestational age (same completed week of pregnancy) and duration of storage of the serum sample (same calendar quarter).
  
  
  RESULTS
  The median uE3, hCG and AFP levels in the twin pregnancies were respectively, 1.67 (95% CI 1.56-1.79), 1.84 (95% CI 1.64-2.07) and 2.13 (95% CI 1.97-2.31) multiples of the median (MoM) for singleton pregnancies at the same gestational age. The variance of values for the three serum markers (expressed in logarithms), and the correlation coefficients between any two, were similar in the twin and singleton pregnancies.
  
  
  CONCLUSIONS
  In maternal serum screening programmes for Down's syndrome dividing uE3, hCG and AFP MoM values in twin pregnancies by the corresponding medians for twin pregnancies will, in expectation, yield a similar false-positive rate in twin pregnancies as in singleton pregnancies.
authors.affiliation: Department of Environmental and Preventive Medicine, St Bartholomew's Hospital Medical College, Charterhouse Square, London.
authors.forename: N
authors.initials: N
authors.lastname: Wald
authors.forename: H
authors.initials: H
authors.lastname: Cuckle
authors.forename: T S
authors.initials: TS
authors.lastname: Wu
authors.forename: L
authors.initials: L
authors.lastname: George
mesh_terms: D006063:Chorionic Gonadotropin / Q000097:blood*; D004314:Down Syndrome / Q000097:blood*; D004964:Estriol / Q000097:blood*; D005260:Female; D006801:Humans; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011272:Pregnancy, Multiple / Q000097:blood*; D011296:Prenatal Diagnosis / Q000379:methods*; D012016:Reference Values; D014427:Twins; D000509:alpha-Fetoproteins / Q000032:analysis
chemical_list: D006063:Chorionic Gonadotropin; D000509:alpha-Fetoproteins; D004964:Estriol