Intertwin Vascular Anastomoses

Monochorionic diamniotic twins with centrally located and closely spaced umbilical cord insertions in the placenta

“…The distance between the cord insertions does not seem to have any particular association with the four types (AA shunt, VV shunt, parenchymal, and component) of anastomoses known to form . Furthermore, it was speculated that most monochorionic placentas had more than one type of anastomosis . In this case, we considered that VV and AA transfusions in placentas with two centrally located UCIs may improve the discordance in birthweight between the twins due to equal placental sharing.…”

“…The number of anastomoses in a monochorionic twin placenta has been reported to be correlated with the distance separating the cord insertion sites . Kellow and Feldstein suggested that monochorionic twins face unique potential complications related to their two cord insertions, such as a higher incidence of velamentous insertions and the intertwining of vascular connections in the single shared placenta.…”

“…On the other hand, Hack et al reported that no associations existed between mortality and anastomosis type, or between type and distance between the UCIs or placental sharing in monoamniotic twins. The distance between the cord insertions does not seem to have any particular association with the four types (AA shunt, VV shunt, parenchymal, and component) of anastomoses known to form . Furthermore, it was speculated that most monochorionic placentas had more than one type of anastomosis .…”

“…In this case, we considered that VV and AA transfusions in placentas with two centrally located UCIs may improve the discordance in birthweight between the twins due to equal placental sharing. These vascular anastomoses have been used to explain the consequences to the surviving twin in cases of the IUD of its cotwin, even if the hemodynamics were balanced to that point .…”

Mechanism of visceral damage in fetofetal transfusion syndrome.

“…[1][2][3] These anastomoses can be direct artery to artery or vein to vein connections on the surface of the placenta, or indirect artery to vein connections within the parenchyma, where a cotyledon is perfused by the artery of one twin but is drained by a vein returning to the other twin. It is as yet unresolved whether the demonstration of an anatomic connection between the circulations after birth can be taken as proof of intermingling of the circulations in utero.…”