title: Does a "vanishing twin" affect first-trimester biochemistry in Down syndrome risk assessment?
abstract: OBJECTIVE
  The purpose of this study was to evaluate the impact of spontaneous reduction in multifetal pregnancy on first-trimester maternal serum biochemistry.
  
  
  METHODS
  We evaluated first-trimester pregnancy associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotropin levels in singleton euploid pregnancies. Biochemical values in pregnancies with evidence of spontaneous reduction were compared to other singleton pregnancies. Mann-Whitney U, Student t test, Fisher exact test, and logistic regression analysis were used for statistical comparison.
  
  
  RESULTS
  There were 41 cases (0.9%) of spontaneous reduction. Though spontaneous reduction was not associated with different levels of either analyte, reduction within 4 weeks was associated with higher levels of both PAPP-A (1.79 vs 1.18; P = .002) and free beta-hCG (1.28 vs 0.96; P = .03) compared with other pregnancies. Spontaneous reduction was associated with a higher frequency of PAPP-A >95th %ile (17.1 vs 4.7%; P = .003) and free beta-hCG >95th %ile (17.1% vs 5.0%; P = .004). Logistic regression identified independent associations between spontaneous reduction and both high PAPP-A and high free beta-hCG.
  
  
  CONCLUSIONS
  Recent spontaneous reduction is associated with higher values of PAPP-A and free beta-hCG. These differences have the potential to affect risk assessment for fetal aneuploidy.
authors.affiliation: Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Weill Medical College of Cornell University, New York, NY, USA. stchasen@med.cornell.edu
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Chasen
authors.forename: Sriram C
authors.initials: SC
authors.lastname: Perni
authors.forename: Mladen
authors.initials: M
authors.lastname: Predanic
authors.forename: Robin B
authors.initials: RB
authors.lastname: Kalish
authors.forename: Frank A
authors.initials: FA
authors.lastname: Chervenak
mesh_terms: D000022:Abortion, Spontaneous / Q000097:blood*; D000328:Adult; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000032:analysis*; D004314:Down Syndrome / Q000175:diagnosis*; D005260:Female; D006801:Humans; D016015:Logistic Models; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000097:blood*; D011272:Pregnancy, Multiple / Q000097:blood*; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis*; D018570:Risk Assessment
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A