title: Early first-trimester free beta-hCG and PAPP-A serum distributions in monochorionic and dichorionic twins.
abstract: BACKGROUND
  In the Netherlands, prenatal screening for trisomy 21 in the first trimester of pregnancy for singletons is conducted through a combined test based on maternal age, nuchal translucency measurement and maternal serum free beta-hCG and PAPP-A. In our clinic risk calculations in twins are currently based on the NT of both fetuses instead of the combined test. In this study we looked at differences in early first-trimester free beta-hCG and PAPP-A between mono- and dichorionic twins.
  
  
  METHODS
  A total of 202 twin pregnant women participated in the study and agreed to donate first-trimester serum for research.
  
  
  RESULTS
  The data of 200 twins with normal outcome were used for setting up reference values for free beta-hCG and PAPP-A. Trisomy 21 was identified in the two remaining pregnancies. The overall median weight-corrected MoM was 1.99 for free beta-hCG, and 2.14 for PAPP-A in all twins. Monochorionic twins have a significantly lower free beta-hCG weight-corrected MoM (1.53 vs 2.11; Mann-Whitney U, p=0.002) and a significantly lower PAPP-A weight-corrected MoM (1.59 vs 2.40; Mann-Whitney U, p=0.003) compared to dichorionic.
  
  
  CONCLUSIONS
  This study strengthened the need to make a distinction between mono- and dichorionic twins for the risk calculation in Down syndrome screening as biochemical markers are significantly lower in monochorionic than in dichorionic twins.
authors.affiliation: Department of Obstetrics and Gynecology, VU University Medical Center Amsterdam, Amsterdam, The Netherlands. I.Linskens@vumc.nl
authors.forename: I H
authors.initials: IH
authors.lastname: Linskens
authors.forename: M D
authors.initials: MD
authors.lastname: Spreeuwenberg
authors.forename: M A
authors.initials: MA
authors.lastname: Blankenstein
authors.forename: J M G
authors.initials: JM
authors.lastname: van Vugt
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D015331:Cohort Studies; D004314:Down Syndrome / Q000097:blood; D005260:Female; D006801:Humans; D010920:Placenta; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000097:blood*; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis*; D012016:Reference Values; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
chemical_list: D015415:Biomarkers; D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A