Purpose of review: 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.
Recent findings: 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.
Summary: 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.