title: First-trimester screening for trisomy 21 using alpha-fetoprotein.
abstract: OBJECTIVE
  To investigate the potential value of adding maternal serum alpha-fetoprotein (AFP) to free β-human chorionic gonadotropin (β-hCG) and PAPP-A and fetal nuchal translucency (NT) thickness in first-trimester screening for trisomy 21.
  
  
  METHODS
  In this case control study, serum AFP was measured in 100 trisomy 21 and 1,500 euploid pregnancies in which screening for trisomy 21 had been performed by a combination of serum free β-hCG and PAPP-A and fetal NT at 11-13 weeks' gestation. We examined the effect of adding AFP on the performance of screening by the combined test.
  
  
  RESULTS
  In the trisomy 21 pregnancies, the median multiple of the normal median AFP, adjusted for gestational age, maternal weight, racial origin, smoking status and method of conception, was significantly reduced (0.7037, 95% CI: 0.6398-0.7739). Adding AFP to the combined test improved the performance of screening and for a risk cut-off of 1 in 100, the false-positive rate was reduced from 2.8 by 0.4% (95% CI: 0.13-0.77%) without a significant change in detection rate.
  
  
  CONCLUSIONS
  Inclusion of serum AFP improves the performance of the first-trimester combined test in screening for trisomy 21.
authors.affiliation: Harris Birthright Research Centre of Fetal Medicine, King's College Hospital, London, UK.
authors.forename: Foteini E
authors.initials: FE
authors.lastname: Bredaki
authors.forename: David
authors.initials: D
authors.lastname: Wright
authors.forename: Pedro
authors.initials: P
authors.lastname: Matos
authors.forename: Argyro
authors.initials: A
authors.lastname: Syngelaki
authors.forename: Kypros H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D004314:Down Syndrome / Q000097:blood / Q000175:diagnosis*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008423:Maternal Age; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011266:Pregnancy-Associated Plasma Protein-A / Q000378:metabolism; D011296:Prenatal Diagnosis; D012307:Risk Factors; D000509:alpha-Fetoproteins / Q000378:metabolism*
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D000509:alpha-Fetoproteins; D011266:Pregnancy-Associated Plasma Protein-A