[SINGLE FETAL DEMISE IN MONOCHORIONIC TWINS]

Single fetal death in a monochorionic twin pregnancy is more frequent than in a dichorionic twin gestation. Due to inter-twin vascular anastomosis in the monochorionic common placenta, the death of one twin causes a drop in blood pressure due to a shift of blood from the survivor to the dead fetus. If the drop of blood pressure is abrupt and serious, the survivor will die soon after (as occurs in 15% of cases). If the drop is less serious, the survivor may sustain ischemic injury (in about 26% of the cases) and if the drop in blood pressure is subtle, the survivor will be intact. Thus, 30% of survivors will sustain serious, mainly brain, injury - a significantly higher incidence than was previously reported. The diagnosis of single fetal demise in a monochorionic twin pregnancy is usually reached at an unknown interval from the co-twin's death and hence, damage has already occurred and there is no need for an untimely delivery of the survivor.