Bipartite monochorionic diamniotic placenta without intertwin vascular anastomoses

抄録

A bipartite placenta develops in 3% of monochorionic diamniotic twin pregnancies. It initially resembles a dichorionic placenta on ultrasonography, but has one chorionic and two amniotic membranes. Almost all monochorionic diamniotic twin placentae have intertwin vascular anastomoses. Older case reports have recorded cases of bipartite placenta in monochorionic diamniotic twins, with vascular anastomoses between the two fetuses－a finding considered to be a reliable marker of a monochorionic placenta. We report two cases of monochorionic diamniotic twin pregnancies, presenting with separate placental masses, and without any intertwin vascular anastomoses. Histological examination revealed a monochorionic and diamniotic intertwin membrane, but a dye injection study in each case demonstrated a complete absence of vascular anastomoses between the two parts of the placenta.