Various types of chorionicity and amniosity (how the baby's sac looks) in monozygotic (identical) twins as a result of when the fertilized egg divides.<unk>  are monozygotic (identical) twins that share the same placenta. If the placenta is shared by more than two twins (see multiple birth), these are<unk>  multiples.<unk>  occur in 0.3% of all pregnancies. Seventy-five percent of monozygotic twin pregnancies are<unk> ; the remaining 25% are dichorionic diamniotic. If the placenta divides, this takes place before the third day after fertilization.
Monochorionic twins
Monoamniotic twins
Locked twins
Conjoined twins
Vestigial twin
Parasitic twin
Craniopagus twins
Vanishing twin