**12. Fetal death**

In general, it is known that multiple pregnancies increase the risk for fetal death. Whenever there is death of one fetus, there is also increased rates of prematurity, neurological sequel and death of the other twin. Chorionicity is determinant in these cases, with more unfavorable prognosis in monochorionic pairs [117].

The vanishing twin syndrome occurs after the sonographic diagnosis of a twin pregnancy, in which a subsequent ultrasound study fails to identify both fetuses. The dead embryo may be completely reabsorbed or even become incorporate into placental membranes, resulting in fetus papyraceous [23, 118].

Later single twin demise in monochorionic twins could also happen due to multiple reasons such as infection, chromosomal or structural anomaly, placental factors or even maternal problems (hypertensive disorder, thrombophilia) [118]. In this scenario, the chance of death of the other fetus and the risk of neurological sequel is around 25% [119]. This can be explained by hemodynamic fluctuations and ischemia, where the blood volume of the living fetus is diverted to the vascular space of the dead fetus, thereby causing multicystic encephalomalacia. Serial ultrasonographic monitoring for brain damage is mandatory and it can be complement‐ ed by magnetic resonance imaging. Although the results were inconsistent, some physicians have reported fetal blood sampling and intrauterine transfusion in the surviving twin [118, 120]. Others highlighted the use of ultrasonographic evaluation of the peak systolic velocity in the middle cerebral artery for detection of fetal anemia [121].

It is important to remember the risk of maternal coagulopathy, which although infre‐ quent, is hard to reverse. Even after single fetal demise, the mode of delivery may be vaginal. The exact time of pregnancy's termination depends on a balance between the need to break the unfavorable gradual evolution of the remaining fetus and the establishment of iatrogenic prematurity [118].
