Identical Twins: All the Important Details

Team Peanut9 months ago6 min read

Identical twins have been intriguing human beings for millenia. From Greek mythology to Shakespeare to the classic that is Parent Trap, the idea of having a real-life doppelganger for a relative is perfect fodder for a good story.

Identical twins

If you are on the road to having identical twins yourself, congratulations! And then congratulations again! Before you know it, seeing double will just be part of your daily routine.

Now, your next job is to find out all about the different types of twins, and what having identical twins means for you and your family.

Monozygotic Twins

If you aim to impress people at dinner parties, whip out this term to describe your identical twosome: monozygotic twins.

While it sounds like it belongs to a delightful duo of sci-fi characters, “monozygotic twins” breaks down to provide a pretty good description of how identical twins are formed. It goes a little something like this:

Mono means one. Zygote is the fertilized ovum that is to become your baby.

Put that together, and monozygotic twins mean twins formed from just one zygote (and therefore just one egg.) So why is this significant? Well, it marks the key difference between the main types of twins.

So, in short, what makes twins identical? Well, they are the product of the same zygote.

What are the 3 types of twins?

1. Identical Twins: Yeah, we know. This is old news to you. You even have a fancy word for them now: monozygotic. Identical twins are formed when a single egg is fertilized, becomes a zygote, and then splits into two. Each side of the split forms into an embryo and then, as time goes on, someone who looks uncannily like their sibling. They often share a placenta in the womb.

➡️ Next up: monozygotic vs dizygotic twins.

2. Fraternal Twins: The next type is fraternal twins, also known as dizygotic twins. If monozygotic twins are formed from a single egg, it follows that dizygotic twins be formed from two different eggs. How does this happen?

When the mama-to-be ovulates, two eggs are released. Some very productive work happens and both are fertilized. The result? Two zygotes! Hence: dizygotic. Hence, not exactly the same and rather like two siblings that share a womb, usually a birthday (unless they choose to be born on either side of midnight) and probably a room.

So those are the two main types of twins. What is the third? While a whole lot less likely, let’s take a look at what’s behind Door Number 3:

3. Semi identical twins: To start, semi identical twins are rare, as in super-duper rare. They are referred to as, wait for it, sesquizygous twins. (To be fair, simply getting that word out of your mouth is probably just as rare.) They happen when your babies somehow share a placenta (like identical twins might) but are not identical (eg. of different genders). While not conclusive, possible theories are that semi identical twins are formed when a single egg is fertilized by two different sperm.

Now, this is something seemingly impossible because usually after an egg is fertilized, it’s like, “Thanks, I’m done!” and shuts the doors for all other sperm to enter. But there you have it. Magic. The research is still quite new in this arena, and not altogether conclusive, but one thing we know is that something like semi identical twins seem to exist. Mind-boggling.

So those are the three types of twins. (It’s important to note that there are some other anomalies—adding up to a full seven types of twins. These include mirror-image twins, mixed chromosome twins, and twins that result from superfecundation and superfetation (whatever that is!).

Yes, once you start delving into the world of twins, you are sure to find astonishing facts around every corner. But, for now, let’s rein it in and return to good ol’ identical twins and the magic that surrounds them.

Monozygotic Twins: Q&A

  • How rare is it to be an identical twin?
    It’s pretty rare. In about every 1000 twin births, about 3 to 5 will be identical twins—and the chances of you having twins that can very accurately pretend to be each other is not correlated directly to your family history. In fact environmental factors and sheer blind luck seem to play a larger role in determining whether you spend the years that follow feeling like you’re living in The Shining.
  • Do identical twins have the same DNA? Yes, yes, yes, they do! 100%. Remember the part about them being formed by the same fertilized egg? They really are two parts of the same whole. Fraternal twins on the other hand only share 50% of their DNA. That means that, in contrast, they can look pretty different and be of different genders.
  • Do identical twins have the same fingerprints? Very interesting question. So, we know that identical twins are the same in pretty much all respects. However, they are still very much unique individuals and one of the defining characteristics of this is their different fingerprints. While their fingerprints may bear a huge resemblance to one another, they are ultimately different. But whyyyy, you ask?

    Well, fingerprints are not a simple product of our DNA. Rather, we develop them in the womb—and the two little beings inside you are going to have a slightly different time in there. That means, no sharing fingerprint-enabled devices—and no taking the fall for one another if up against the law.

Finally, if you are having identical twins, it’s important that you keep up with regular check-ups and talk to your healthcare provider if anything feels a little off. Because the process of growing identical twins is extraordinary, the demands it takes on your body are upped significantly.

For this reason, twins are often born premature—around 37 weeks—and can cause some health issues for both them and you.

Motherhood is one heck of an adventure. Motherhood when it involves identical twins? Well. It’s the equivalent of ordering a double. We wish you double the love on this adventure. You’ve got this!

Read also:
How to Conceive Twins
A Short Guide to Identical Triplets
Twin Telepathy: What’s the Truth?
Identical vs Fraternal Twins: What’s the Difference?
Do Identical Twins Have the Same DNA?