title: Optimal interval for ultrasound surveillance in monochorionic twin gestations.
abstract: OBJECTIVE
  To examine the association between interval from previous ultrasonogram to diagnosis of twin-twin transfusion syndrome and stage at diagnosis.
  
  
  METHODS
  We reviewed all monochorionic twins undergoing evaluation for twin-twin transfusion syndrome in our ultrasound department from 2001 to 2008. Cases of twin-twin transfusion syndrome were categorized as early (Quintero stages I and II) or late (Quintero stages III-V). The gestational age at diagnosis and the interval from the last ultrasonogram were recorded. The interval was categorized as 14 days or less or greater than 14 days. Pregnancies diagnosed with twin-twin transfusion syndrome at the initial ultrasonogram were categorized as greater than 14 days. The univariable association between interval from last scan and twin-twin transfusion syndrome stage was determined by χ2. P<.05 was considered significant.
  
  
  RESULTS
  One-hundred eight monochorionic twin pregnancies were identified, and 42 met criteria for twin-twin transfusion syndrome: 24 with early stage and 18 with late stage. The median gestational age at diagnosis was 19 6/7 (15 3/7-36 3/7) weeks. Twin-twin transfusion syndrome was more likely to be diagnosed at a later stage with an ultrasound interval greater than 14 days (P=.004). Two cases (11.8%) of late twin-twin transfusion syndrome were diagnosed in pregnancies with an ultrasound interval of 14 days or less.
  
  
  CONCLUSIONS
  An interval of greater than 14 days from previous ultrasonogram was strongly associated with detection of higher-stage twin-twin transfusion syndrome. These data suggest that a maximum surveillance interval of 14 days for monochorionic twins may lead to earlier stage at diagnosis, earlier intervention, and better outcomes.
  
  
  METHODS
  III.
authors.affiliation: From the University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania.
authors.forename: Heidi L
authors.initials: HL
authors.lastname: Thorson
authors.forename: Devon M
authors.initials: DM
authors.lastname: Ramaeker
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Emery
mesh_terms: D000328:Adult; D005260:Female; D005330:Fetofetal Transfusion / Q000000981:diagnostic imaging*; D005865:Gestational Age; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy; D012189:Retrospective Studies; D014430:Twins, Monozygotic; D016216:Ultrasonography, Prenatal / Q000592:standards; D055815:Young Adult