The survival rate for<unk>  has been shown to be as high as 81% to 95% in 2009 with aggressive fetal monitoring, although previously reported as being between 50% to 60%. Causes of mortality and morbidity include: *Cord entanglement: The close proximity and absence of amniotic membrane separating the two umbilical cords makes it particularly easy for the twins to become entangled in each other's cords, hindering fetal movement and development. Additionally, entanglement may cause one twin to become stuck in the birth canal during labor and expulsion. Cord entanglement happens to some degree in almost every<unk>  pregnancy. * Cord compression: One twin may compress the other's umbilical cord, potentially stopping the flow of nutrients and blood and resulting in fetal death. * Twin-to-twin transfusion syndrome (TTTS): One twin receives the majority of the nourishment, causing the other twin to become undernourished. TTTS is much more difficult to diagnose in<unk>  than diamniotic ones, since the standard method otherwise is to compare the fluid in the sacs. Rather, TTTS diagnosis in<unk>  relies on comparing the physical development of the twins.
Monoamniotic twins
Monochorionic twins
Locked twins
Conjoined twins
Parasitic twin
Craniopagus twins
Vanishing twin
Vestigial twin