Late onset of discordant growth in a monochorionic twin pregnancy: vascular anastomoses determine fetal growth pattern and not placental sharing.

Twin-twin transfusion syndrome in monochorionic twin pregnancies has a complex and variable clinical presentation. We present the first documented case where two unidirectional arteriovenous anastomoses connecting the donor twin's larger with the recipient's smaller placental part produce late onset of discordant growth and subsequent twin-twin transfusion syndrome. We conclude that the haemodynamic effects of the anastomoses caused the observed discordant fetal development and not the unequally shared placenta.