title: Monochorionic diamniotic twin pregnancy: timing and duration of sonographic surveillance for detection of twin-twin transfusion syndrome.
abstract: OBJECTIVE
  Twin-twin transfusion syndrome complicates up to 15% of monochorionic diamniotic gestations. Current recommendations for sonographic surveillance in monochorionic diamniotic pregnancies for detection of twin-twin transfusion syndrome vary. Our objective was to determine an appropriate frequency of sonographic surveillance to optimize detection of twin-twin transfusion syndrome in monochorionic diamniotic gestations.
  
  
  METHODS
  A retrospective cohort analysis of all nonanomalous monochorionic diamniotic twins delivered at the University of North Carolina over a 9-year period was performed. The rate and gestational age of twin-twin transfusion syndrome onset were calculated. The time to the diagnosis of twin-twin transfusion syndrome was evaluated by a Kaplan-Meier survival curve; clinical factors at initial sonography were examined for their use in prediction of twin-twin transfusion syndrome.
  
  
  RESULTS
  Of the 577 twin deliveries, 145 (25%) were monochorionic diamniotic and included for analysis. The rate of twin-twin transfusion syndrome was 17.93% (n = 26). The mean frequency of surveillance ± SD before diagnosis of twin-twin transfusion syndrome was 3.1 ± 2.1 weeks. The mean gestational age at diagnosis of twin-twin transfusion syndrome was 21.3 ± 3.4 weeks (range, 15-29 weeks). Both a discordant maximum vertical amniotic fluid pocket (>65% difference) and a discordant estimated fetal weight (>25% difference) at initial sonography showed a significantly shorter time to diagnosis of twin-twin transfusion syndrome (P < .0001).
  
  
  CONCLUSIONS
  Evaluation for twin-twin transfusion syndrome should begin in the second trimester. Weekly surveillance for those pregnancies with estimated fetal weight or maximum vertical pocket discordance is recommended. For those with a concordant estimated fetal weight and maximum vertical pocket, sonographic evaluation every 2 weeks is warranted to 28 to 30 weeks. After that, development of twin-twin transfusion syndrome is less likely, and a different paradigm of antenatal testing may be reasonable.
authors.affiliation: Department of Obstetrics and Gynecology, University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, North Carolina, USA.
authors.forename: Alissa
authors.initials: A
authors.lastname: Carver
authors.forename: Sina
authors.initials: S
authors.lastname: Haeri
authors.forename: Julie
authors.initials: J
authors.lastname: Moldenhauer
authors.forename: Honor M
authors.initials: HM
authors.lastname: Wolfe
authors.forename: William
authors.initials: W
authors.lastname: Goodnight
mesh_terms: D005260:Female; D005330:Fetofetal Transfusion / Q000000981:diagnostic imaging* / Q000401:mortality*; D005865:Gestational Age; D006801:Humans; D008297:Male; D009657:North Carolina / Q000453:epidemiology; D011159:Population Surveillance / Q000379:methods*; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D015995:Prevalence; D012307:Risk Factors; D015996:Survival Rate; D014430:Twins, Monozygotic / Q000706:statistics & numerical data*; D016216:Ultrasonography, Prenatal / Q000379:methods*