In addition to a shared placenta,<unk>  also have their circulatory systems intermingled in random and unpredictable circulatory anastomoses. This can cause disproportionate blood supply, resulting in twin-to-twin transfusion syndrome (TTTS) in 20% of MoDi pregnancies. This is the main complication of<unk> . The 80% of MoDi pregnancies without TTTS still have high rates of birth weight discordance, fetal growth restriction, prematurity and resultant cesarean section deliveries. One twin may also fail to develop a proper heart and become dependent on the pumping activity of the other twin's heart, resulting in twin reversed arterial perfusion. If one twin dies in utero, blood accumulates in that twin's body, causing exsanguination of the remaining twin. In the case of monoamniotic twins the risk of complications is substantially higher because of additional potential umbilical cord entanglement and compression. However, the perinatal mortality of<unk>  is fairly low.
Monochorionic twins
Monoamniotic twins
Locked twins
Conjoined twins
Vestigial twin
Parasitic twin
Craniopagus twins
Vanishing twin