Fraternal vs Identical twins: Common types of twins

If you’ve just found out you’re expecting two little bundles of joy instead of one, CONGRATS! 🥳

Double the joy… and double the questions! Not to worry, we’re here to help.

Here’s a simple breakdown of the most common types of twins.

Fraternal twins (Dizygotic)

Fraternal or non-identical twins are the most common type of twins worldwide. These two are more like regular siblings who just decided to rent the womb at the same time. Fraternal twins share only half of their genomes. The scientific term “dizygotic” refers to two different eggs, which are fertilized by two different sperm. This can happen because two eggs were released by the ovaries instead of just one.

Fun facts:
– Can be the same or different sexes
– No more alike than any other siblings

Identical twins (Monozygotic)

These two are the ultimate copy-paste. Identical twins come from one fertilized egg (monozygotic) that splits into two. Basically, the body said, “Let’s make a human!” and then “Make it a double!” They share all the same genetic material and are genetically identical. They usually look super similar, but their personalities can be as different as ketchup and mustard.

Fun facts:
– Same sex
– Same DNA

Mirror twins

These twins are a rare, quirky sub-type of identical twins. They originate from the same egg, but the egg splits a little later than usual, and the twins develop as mirror images of each other. Think: one’s a lefty, the other’s a righty; one has a freckle on the left cheek, the other on the right; opposite birthmarks. Basically, it’s like nature decided to have some fun with symmetry.

Conjoined twins

Conjoined twins are also a sub-type of identical twins. They are born with their bodies physically connected. Doctors do not fully understand how this occurs but there are theories, such as the identical twin egg not splitting fully. This complicated phenomenon is extremely rare.

There are other types of twins but the ones listed above are the most common.

MoMo, MoDi and DiDi twins (huh?)

Don’t worry, this isn’t a new language you missed on Duolingo. Twinning is quite complex, so there are a few terms that doctors use to describe how twins are set up in the womb.

Fraternal and identical are categories of twins based on the number of eggs (something called zygosity), but twins can also be categorised based on chorionicity and amnionicity.

These terms describe how the twins share the placenta and amniotic sacs. “Monochorionic” means a single placenta, whereas “Dichorionic” means two. Monoamniotic” means one sac, whereas “Diamniotic” means two. Simple, right? 😆

There are three possible combinations of sacs and placentas:

• DiDi (Dichorionic/Diamniotic)
  Two placentas, two sacs. Like next-door neighbours with their own rooms. They are the most common form of twins and can be either identical or fraternal.
• MoDi (Monochorionic/Diamniotic)
  One placenta, two sacs. Basically housemates that share snacks, but sleep in separate rooms. MoDi twins are always identical.
• MoMo (Monochorionic/Monoamniotic)
  One placenta, one sac. Very close roommates that share everything. MoMo twins are also always identical.

Frequently asked questions about twins

What does this all mean for you?

Whether your twins are identical or fraternal, MoMo, MoDi or DiDi, you’re about to experience double the kicks, double the laundry and of course, double the love!

It might sound cliché, but honestly, nothing compares to the magic of twins.

Just remember: you’ve got this.

And there’s an entire twin parent community (and coffee) to support you along the way 💪💕

So, are you ready for twins? Take this fun quiz to find out