title: Second-trimester maternal serum free-beta-human chorionic gonadotropin and alpha-fetoprotein levels in normal twin and singleton pregnancies: a report of local Chinese population.
abstract: OBJECTIVE
  The study evaluated the differences between Chinese normal twin and singleton pregnancies in the levels of maternal serum free-beta-human chorionic gonadotropin (free beta-hCG) and alpha-fetoprotein (AFP) used in second-trimester Down syndrome (DS) screening.
  
  
  METHODS
  The concentrations of maternal serum markers of 456 twin pregnancies and 12 067 singleton controls in gestational 15 to 20 weeks were measured by time-resolved fluoroimmunoassay, and the levels of markers were compared between the twins and singletons.
  
  
  RESULTS
  Significant differences were found between the levels of free beta-hCG in twins and twice of those in singletons in 16, 17 and 19 gestational weeks (p < 0.05 for all); while considering AFP, significant differences were found in 16 and 19 gestational weeks (p < 0.05 for both). No correlations were found in twins between the levels of markers and maternal weights in most gestational weeks (Free beta-hCG: p > 0.05 for 15 to 18 and 20 gestational weeks; AFP: p > 0.05 for 16 to 20 gestational weeks).
  
  
  CONCLUSIONS
  The Chinese gestational age-specific levels of maternal serum markers in normal twins are not twice as those in singletons. The current weight-correction model for DS screening may be not feasible for twins.
authors.affiliation: Women's Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
authors.forename: Zhenwei
authors.initials: Z
authors.lastname: Xie
authors.forename: Shiming
authors.initials: S
authors.lastname: Lu
authors.forename: Yuning
authors.initials: Y
authors.lastname: Zhu
authors.forename: Yali
authors.initials: Y
authors.lastname: Sun
authors.forename: Yu
authors.initials: Y
authors.lastname: Jin
mesh_terms: D044466:Asian People; D002681:China; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D004314:Down Syndrome / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008403:Mass Screening; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000097:blood*; D011296:Prenatal Diagnosis; D012016:Reference Values; D014427:Twins / Q000097:blood*; D000509:alpha-Fetoproteins / Q000378:metabolism*
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D000509:alpha-Fetoproteins