title: Perinatal complications of monochorionic placentation.
abstract: OBJECTIVE
  The aim of this review is to update readers on the pathophysiology of twin-twin transfusion syndrome and monochorionic diamniotic twins with discordant growth restrictions.
  
  
  RESULTS
  Discordant nuchal translucency of at least 20% can be used to screen for early loss and twin-twin transfusion syndrome. Recent Doppler-based longitudinal flow study through arterio-venous anastomoses shows that it is their size rather than their numbers and direction that determine transfusional complication in monochorionic twins. High plasma level of renin-angiotensin system effectors and increased placental renin mRNA and protein suggest that the recipients are exposed to high levels of placental-derived rennin-angiotensin system effectors. Recently discovered deep subchorionic vascular anastomoses have clinical implications for laser treatment for twin-twin transfusion syndrome. Rate of cerebral palsy among survivors is 5-17%. In monochorionic diamniotic twins with transmitted patterns in the umbilical artery, there is increased risk of sudden death and abnormal cranial lesions in the larger cotwins.
  
  
  CONCLUSIONS
  The role of the rennin-angiotensin system and the relationship between deep vascular anastomoses and perinatal outcome in twin-twin transfusion syndrome need further evaluation. In monochorionic twins with transmitted patterns in the umbilical artery Doppler studies, delivery at 32 weeks is being advocated.
authors.affiliation: Directorate of Women & Children, Barts and Royal London NHS Trust, Whitechapel, London, UK. ling.wee@bartsandthelondon.nhs.uk
authors.forename: Ling Yee
authors.initials: LY
authors.lastname: Wee
authors.forename: Ida
authors.initials: I
authors.lastname: Muslim
mesh_terms: D001783:Blood Flow Velocity / Q000502:physiology*; D002547:Cerebral Palsy / Q000453:epidemiology / Q000209:etiology; D005260:Female; D005312:Fetal Blood / Q000502:physiology*; D005330:Fetofetal Transfusion / Q000000981:diagnostic imaging / Q000473:pathology*; D005333:Fetus / Q000098:blood supply*; D006439:Hemodynamics; D006801:Humans; D017078:Laser-Doppler Flowmetry / Q000379:methods; D011247:Pregnancy; D014429:Twins, Dizygotic; D016216:Ultrasonography, Prenatal / Q000379:methods*