Placental vasculature in the pathogenesis of fetal mortality and morbidity in multiple pregnancies

If a monochorionic (MC) twin dies in utero, its co-twin may experience a variety of clinical outcomes, ranging from no sequelae to severe neurological damage or death. It is likely that the existing anastomotic pattern on the shared MC placenta primarily determines outcome. Sequelae are assumed to result from: exsanguination of the survivor into the dead twin’s circulation along anastomoses; transfusion

of active compounds such as clotting factors or interleukins from the dead twin into the survivor’s body; or other causes. If no such sequelae develop in the co-twin, either the MC placenta lacks anastomoses (about 4% of cases) or, more important, exsanguination of the survivor remains limited because there is a favorable return anastomotic path from the dead twin to the survivor.