title: Hypothesis acardiac twin pregnancies: Pathophysiology-based hypotheses suggest risk prediction by pump/acardiac umbilical venous diameter ratios.
abstract: BACKGROUND
  A total of 75% of monozygotic twins share 1 monochorionic placenta where placental anastomoses cause several serious complications, for example, acardiac twinning. Acardiac twins lack cardiac function but grow by perfusion of arterial blood from the pump twin. This rare pregnancy has 50% natural pump twin mortality but accurate risk prediction is currently impossible. Recent guidelines suggest prophylactic surgery before 18 weeks, suggesting 50% unnecessary interventions. We hypothesize that (1) adverse pump twin outcome relates to easy-to-measure pump/acardiac umbilical venous diameter (UVD) ratios, representing acardiac perfusion by the pump's excess cardiac output. This hypothesis suggests that (2) UVD-ratios are large, mildly varying in cases without complications but small and decreasing when complications develop, thus predicting that (3) UVD-ratios may allow risk prediction of pump twins. In this exploratory clinical pilot, we tested whether UVD-ratio measurements support these predictions.
  
  
  METHODS
  We included 7 uncomplicated (expectant management), 3 elective surgical, and 17 complicated cases (pump decompensation, emergency intervention/delivery or demise). Nine UVD-ratios were measured sonographycally and 18 by pathology.
  
  
  RESULTS
  Uncomplicated cases have larger, two serial measurements showing mildly varying UVD-ratios; elective surgical cases show larger UVD-ratios; complicated cases have smaller, two serial measurements showing decreasing UVD-ratios. There were no false-positives, no false-negatives and noncrossing linear trendlines of uncomplicated and complicated cohorts.
  
  
  CONCLUSIONS
  Our data provide first evidence that UVD-ratios allow risk prediction of pump twins. More early uncomplicated and late complicated cases are needed, for example, in a prospective trial, before the separation between uncomplicated and complicated cohorts is accurate enough to support a well-founded decision on (early) intervention.
authors.affiliation: Department of Biomedical Engineering & Physics, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Martin J C
authors.initials: MJ
authors.lastname: van Gemert
authors.affiliation: Department of Obstetrics and Gynecology, University Medical Center, Utrecht, The Netherlands.
authors.forename: Lourens R
authors.initials: LR
authors.lastname: Pistorius
authors.affiliation: Department of Pathology, University of California at San Diego, San Diego, California.
authors.forename: Kurt
authors.initials: K
authors.lastname: Benirschke
authors.affiliation: Department of Public Health and Obstetrics and Gynecology, Erasmus Medical Center, Rotterdam, The Netherlands.
authors.forename: Gouke J
authors.initials: GJ
authors.lastname: Bonsel
authors.affiliation: Department of Obstetrics and Gynecology, Radboud University Medical Center, Nijmegen, The Netherlands.
authors.forename: Frank P H A
authors.initials: FP
authors.lastname: Vandenbussche
authors.affiliation: Department of Obstetrics and Gynecology, Gelre Teaching Hospitals, Apeldoorn, The Netherlands.
authors.forename: K Marieke
authors.initials: KM
authors.lastname: Paarlberg
authors.affiliation: Department of Biomedical Engineering & Physics, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Jeroen P H M
authors.initials: JP
authors.lastname: van den Wijngaard
authors.affiliation: Department of Pathology, Wilhelmina Children's Hospital, University Medical Center, Utrecht, The Netherlands.
authors.forename: Peter G J
authors.initials: PG
authors.lastname: Nikkels
mesh_terms: D000013:Congenital Abnormalities / Q000196:embryology*; D005260:Female; D006321:Heart / Q000196:embryology*; D006330:Heart Defects, Congenital / Q000196:embryology*; D006801:Humans; D010920:Placenta / Q000098:blood supply* / Q000502:physiology; D011247:Pregnancy; D059285:Pregnancy, Twin; D012189:Retrospective Studies; D014430:Twins, Monozygotic; D014471:Umbilical Veins / Q000503:physiopathology*
keywords: acardiac twin pregnancy; pathophysiology; risk prediction of pump twin; serial UVD-ratio measurement; twin reversed-arterial perfusion sequence; umbilical venous diameter ratio (UVD-ratio)