Olsen Twins

Monoamniotic twins are always monozygotic (identical twins).
The survival rate for monoamniotic twins is somewhere between 50% to 60%.
Consequently, if twins are monoamniotic that means that the two babies will be sharing a placenta and as a result, due to the small capacity of sharing a sac, the umbilical cord has an increased chance of being tangled around the babies. Because of this, there is an increased chance that the newborns may be miscarried or suffer from cerebral palsy due to the lack of oxygen.
Monoamniotic twins occur when the split takes place after the ninth day after fertilization.