azraili:sixpenceee:Twin to Twin Transfusion Syndrome occurs only in identical twins that share one p
azraili:sixpenceee:Twin to Twin Transfusion Syndrome occurs only in identical twins that share one placenta. Blood vessels from the shared placenta connect the twins and, for reasons that are not clear, the blood flow between the twins becomes unbalanced, resulting in one twin not getting enough blood and the other becoming overloaded with too much blood. The exact causes are unknown. This can be a danger to both twins and even the mother. (Source)That is terrifying -- source link