How Are Identical Twins Formed?

How are identical twins formed? Identical twins are formed when a single egg is fertilized by one sperm cell and then divides into two. The split seems to happen at random to women of all race and sizes. The twin babies are genetically nearly identical, however identical twins fingerprints are different. Identical twins are almost always of the same sex, except in a few very rare cases, where identical twins have been born male and female. Knowing how identical twins are formed and develop in the womb, can help you in order to determine whether or not your twin babies are identical or fraternal.

Di-di – fraternal or identical twins

Identical twins in the womb can have their own separate inner and outer membrane and each have a placenta. They are nicknamed di-di twins (dichorionic diamniotic). Identical di-di twins are sometimes mistaken for being fraternal, as all fraternal twins are di-di twins, whereas this goes for only one third of all identical twins.

Mo-di – identical twins

Identical twins can also be monochorionic diamniotic, named mo-di twins. The twin babies share a single placenta and one single outer membrane, but they each have their own separate inner membrane. This is the case for two thirds of all identical twins making it the most common type of identical twin. Mo-di twins can’t be fraternal. Nevertheless, be aware that placentas can fuse together, fooling health care providers to believe that fraternal di-di twins are in fact identical.

Mo-mo – identical twins

Mo-mo (monochorionic monoamniotic) twins are extremely rare. The twin babies share one single placenta and share both the outer and inner membrane. They only account for about one percent of all identical twins and can never be fraternal.

How are identical twins formed? We hope you now know and that we’ve answered your questions. Otherwise leave a comment below this article. If you’re still not sure whether or not your twin babies are identical or fraternal then consider trying out our Twin Test.