title: Screening for Down syndrome in dichorionic twin pregnancies conceived by in vitro fertilization (IVF): a clinical pilot study to confirm the laboratory methods.
abstract: OBJECTIVE
  The corrections necessary to estimate the risk for Down syndrome in twin pregnancies have been pointed out. We performed a nested controlled study to evaluate the validity of these corrections in dichorionic twins conceived by IVF.
  
  
  METHODS
  Detailed clinical data was collected from the medical records. Twins were matched with a contemporaneous cohort of spontaneously conceived singleton pregnancies that serve as reference in a 1 to 4 ratio. All patients had their entire obstetrical care at our Hospital. The Student t-test was used for group comparisons and a p-value <0.05 was considered significant.
  
  
  RESULTS
  Nineteen sets of normal twins concordant in size and with appropriate weight for gestational age were matched with 80 normal and mature newborns. Significant differences between groups were found for maternal age, gestational age at delivery and newborn weight (all p < 0.01). No statistical differences were noted for the levels of the biochemical markers expressed as multiples of the median. However, a 15 % closer approximation to the laboratory median for PAPP-A and a 10 % closer approximation to the laboratory median for free β-hCG was evident in twins when compared to the reference group.
  
  
  CONCLUSIONS
  These findings support the methods used to estimate the risk for Down syndrome in dichorionic twin pregnancies conceived after IVF. A future study with a larger sample size could confirm if the laboratory corrections done on the combined screening test improve the predictability of Down syndrome in dichorionic twin pregnancy conceived by IVF when compared to singleton pregnancies.
authors.affiliation: Departments of Obstetrics, Gynecology and Reproductive Sciences, Rutgers-Robert Wood Johnson Medical School, New Brunswick, NJ, USA.
authors.forename: Lissa
authors.initials: L
authors.lastname: Francois
authors.forename: Lindsay
authors.initials: L
authors.lastname: Kugler
authors.forename: Jacobo L
authors.initials: JL
authors.lastname: Santolaya
authors.forename: Revital
authors.initials: R
authors.lastname: Faro
authors.forename: Valeria
authors.initials: V
authors.lastname: Di Stefano
authors.forename: Lena
authors.initials: L
authors.lastname: Merjanian
authors.forename: Joaquin
authors.initials: J
authors.lastname: Santolaya-Forgas
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D019411:Clinical Laboratory Techniques / Q000379:methods; D004314:Down Syndrome / Q000175:diagnosis*; D005260:Female; D005307:Fertilization in Vitro / Q000706:statistics & numerical data; D006801:Humans; D010865:Pilot Projects; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000097:blood; D059285:Pregnancy, Twin / Q000097:blood*; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis; D011296:Prenatal Diagnosis / Q000379:methods*; D014429:Twins, Dizygotic
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A