A case of fetal twin-to-twin cytomegalovirus infection through a dichorionic diamniotic (DiDi)-fused placenta prompted our search for possible vascular anastomoses in this type of placenta. This case and three additional DiDi-fused placentas were studied with gross (macro) sections and a three-dimensional (3D) stereomicroscopic technique. Two twins were dizygotic (they differed in gender and blood groups) and the other two were probably monozygotic. Macrosections and 3D-image analysis demonstrated side-to-side connections between small subchorionic vessels. These findings demonstrate that vascular anastomoses are present in DiDi-fused placentas.
Vascular anastomoses in placentas of twin fetuses are well described in cases of diamniotic monochorionic (DiMo) and monoamniotic monochorionic (MoMo) placentas, in which they constitute an important prognostic factor for the outcome of multiple pregnancies (1). Vascular anastomoses have only rarely been described in diamniotic dichorionic (DiDi)-fused placentas (2–4). Recently we observed a case (propositus case) of fetal twin-to-twin cytomegalovirus (CMV) infection through a DiDi-fused placenta. Although amniotic fluid collected at the 21st week of gestation indicated CMV infection in only one baby, evidence of CMV infection was present in both babies at birth (5). This observation prompted our search for possible vascular anastomoses in DiDi-fused placentas.