Very rare & because share same genes & in utero environment they are more identical than typical identical twins! And, they were born on Mother’s Day… meant to be?
Typically, identical twins are not 100% identical because of different genetic expression likely based on differing in utero hormonal and other experiences, as well as extremely minor genetic mutations. But in the case of these newborns, their in utero exposure should be identical, making them even more similar than typical monozygotic twins that experience different amniotic sacks. An important aside: they will still have different personalities…like all twins… which means much if not most of our personality development is due to post-birth environmental reasons. Probably the biggest reason? Living with having to differentiate from a sibling!