Identical, fraternal, half-identical, inverted twins, chromosome twins mixed, superfecondation and superfiguration.
If the first two cases are very common, the others are quite rare. Inverted twins usually have “mirrored” images of their features, such as reverse-oriented hair, a birthmark on the right shoulder for one, and on the left for the other, one of the twins. can be right-handed and the other left-handed (22% of twins are left-handed, versus 10% on average), etc.
About 1 in 250 pregnancies result in identical twins. Nigeria has the highest rate of multiple births and identical twins. It is in China that it is the lowest, on average 1 in 300.