Craniopagus twins the set of twins as being a unique malformation and a punishment from their mother’s mistake. Furthermore, in Ambroise Pare’s book, "On Monsters and Marvels", various types of "supernatural" twinning are illustrated and described as "monstrous and marvelous creatures that proceed from the judgment of God". This published history suggests that conjoined twins, and in specific craniopagus twins, were viewed as literal monsters during that era. Craniopagus twins Craniopagus twins are conjoined twins that are fused at the cranium. This condition occurs in about 10–20 babies in every million births in the United States. Among this small group, cephalic conjoining,
Monoamniotic twins Monoamniotic twins Monoamniotic twins are identical twins that share the same amniotic sac within their mother’s uterus. Monoamniotic twins are always identical, always monochorionic and are usually termed Monoamniotic-Monochorionic ("MoMo" or "Mono Mono") twins. They also share the placenta, but have two separate umbilical cords. Monoamniotic twins develop when an embryo does not split until after formation of the amniotic sac, at about 9-13 days after fertilization. Monoamniotic triplets or other monoamniotic multiples are possible, but extremely rare. Other obscure possibilities include multiples sets where monoamniotic twins are part of a larger gestation such as triplets, quadruplets, or more. Monoamniotic