Placental injection studies in twin gestation.

Vascular communication between placental vessels can occur when there is a fused placental mass in twin gestation. The presence of anastomotic channels can lead to the twin-twin transfusion syndrome in the fetuses. A study was conducted on 278 twin pairs to determine the incidence of vascular communication in fused twin placentas and the frequency of twin-twin transfusion syndrome. Anastomotic communication was found almost universally in monochorionic placentation and very rarely with dichorionic placentas. Twin-twin transfusion syndrome occurred uncommonly despite the high frequency of occurrence of cross-placental vascular communication. Misdiagnosis of intrauterine growth retardation in one twin can be avoided by determination of chorionicity by inspection of the placentas of twin gestation.