Identical vs Fraternal Twins: What’s the Difference?

So, twins it is. But do you know what type of twins you’re having?

Identical vs fraternal twins ‒ what’s the difference?

Twice the excitement, twice the fun, twice the love, twice the… tiredness.

But let’s get down to the nitty-gritty details of twins.

Identical vs fraternal twins – what actually is the difference?

You’ll see some twins look like peas in a pod – so similar that even their mamas can’t always tell them apart.

Then there are the others: just as cute, but clearly distinct.

So how do you tell the difference between identical and fraternal twins? Take a guess!

The difference comes down to what happens when the egg and sperm meet.

In identical twins, the egg gets fertilized and then splits – making two (or three, why not?) identical babies.

In fraternal twins, two different eggs get fertilized, producing two babies with different looks and often different genders.

That’s the long and short of it.

But let’s look at identical vs fraternal twins in a little more detail.

In this article: 📝

What is the difference between identical and fraternal twins?

So, what’s actually the difference between fraternal and identical twins?

Well, mamas, pens at the ready.

There are some technical terms coming up…

Monozygotic vs dizygotic twins

While we refer to them as identical and fraternal twins, scientists do things differently.

To them, identical twins are better known as monozygotic twins.

Fraternal twins, meanwhile, take the name dizygotic twins.

Why? A zygote is the scientific term used for a fertilized egg with sperm inside.

In identical twins, there’s one of these (mono meaning ‘one’).

In these cases, one fertilized egg splits in two to make two genetically identical babies.

Now, because identical twins come from the same egg, they’re most often the same sex, either both male, or female. There are very rare exceptions to this rule.

In fraternal twins, there are two zygotes (di meaning ‘two’) – and the babies produced are genetically different, like non-identical siblings.

Fraternal twins can be a male and female or the same sex.

Note🤓: It’s important to remember that sex and gender aren’t the same. Identical twins may be assigned the same sex at birth, but it may not align with their gender identity as they age.

This may sound all good and academic.

Now, to the basics of their growth.

Fundamentally, the difference between fraternal and identical twins comes down to those zygotes.

But this little difference also affects the practical matters of birth.

Because identical twins come from one egg, they share the same placenta and the same amniotic sac (the bag of fluid that protects the fetus in the womb).

Fraternal twins, on the other hand, will have separate placentas and separate amniotic sacs.

These things are quite handy to know.

Even if, like most mamas of twins, you may opt for a c-section birth.

Identical vs fraternal twins ultrasound

So now we know the technical difference between identical and fraternal twins, how do they both look in their ultrasound?

Well, it all comes down to whether the twins share the same placenta and amniotic sac or not.

If there’s one placenta and one amniotic sac, you’re looking at monozygotic (identical) twins.

If each baby has their own placenta and amniotic sac, then they’re dizygotic (fraternal) twins.

The best bit? The fraternal vs identical twins ultrasound can be done as early as 8 weeks, for your first-trimester ultrasound.

What is the difference between fraternal and semi-identical twins?

Hold up. Semi-identical twins?

Semi-identical twins (also known as sesquizygotic twins) are actually very rare ‒ just two cases recorded ‒ ever!

Semi-identical twins happen when two sperm manage to fertilize the same egg, which then splits in two.

These sesquizygotic twins end up with all the same chromosomes as the person carrying them, and about half the chromosomes from their other parent.

So you can have semi-identical twins that share a placenta and amniotic sac, like identical twins, but they may be two different sexes and have a few visible differences between them, like fraternal twins.

What are more rare, fraternal or identical twins?

So now we know how rare semi-identical twins are, which is rarer between fraternal and identical twins?

Well, all in all, according to the US Center for Disease Control and Prevention, identical and fraternal twins account for about 32.6 of every 1000 live births in the US.

That means your chances of having identical or fraternal twins are about 3.26%.

However, this rate changes across the world – and it may be higher if you’re having IVF or if you’re over 35.

According to the NHS, while 1 in 80 births in the UK are identical or fraternal twins, that increases to 1 in 5 after IVF.

Between fraternal and identical, though, it’s the fraternal twins that are more common.

And it’s more common for you to have twins of opposite genders than of any other gender pairing.

All pregnant women have the same likelihood of giving birth to identical twins ‒ about 1 in 250.

Fraternal twins are more likely in mamas who have had twins before – and in those who have other women with twins in the family. This is because it’s hereditary.

But in the case of identical twins, it’s more of a surprise, as it’s not hereditary. 🫣

Women over 35 are also more likely to give birth to fraternal twins – as they are more likely to release more than one egg during ovulation.

And especially if you opt for a double embryo transfer during IVF, you are more likely to give birth to fraternal twins.

Can fraternal twins look identical?

That’s most of the science covered.

But how are you to know if you have had identical or fraternal twins?

And can fraternal twins look identical even if they are not genetically identical?

To start with, fraternal twins can look pretty similar, yes.

But they can also look completely different.

Fraternal twins follow siblings generally: they can be different sexes, have different hair colors, eye colors, sizes, and facial features (even the genetic similarity is that of siblings).

But you’ll almost certainly be able to tell they are siblings.

How to tell if twins are fraternal or identical?

However, you may find that, as newborn babies, you can’t really tell whether your Tweedledum and Tweedledee are identical or not.

To find out after birth, the placenta can be a good place to start.

Whether one or two is present can be a good sign of whether you’ve been blessed with identical or fraternal twins (although it is not always an accurate method).

Otherwise, health services recommend using a DNA test to see what’s what.

It is generally recommended, though, to find out during pregnancy whether you are dealing with fraternal or identical twins.

It’s important to know because, if your twins are sharing the same placenta and amniotic sac, complications are just slightly more likely to occur.

Similarly, knowing whether they are identical or fraternal twins is important knowledge for later in life too.

Identical twins are more likely to have the same illnesses, for example.

And, let’s be honest, it is just quite nice to know.

What are the 3 types of twins?

Identical vs fraternal twins vs…? Is there a third type of twins?

Well, we’ve already covered the three main types of twins: identical, fraternal, and semi-identical.

But there are actually seven different types of twins.

There are also mirror-image twins, which are also rare, like semi-identical twins ‒ these twins are literally the mirror image of each other!

Then you have mixed chromosome twins, which start as fraternal twins ‒ two separate fertilized eggs, which then fuse together.

Next up is superfetation ‒ also very uncommon ‒ which is essentially you getting pregnant while pregnant. Yup, it’s possible!

Finally, we have superfecundation, which is where you have twins with two different fathers ‒ again, stranger things have happened!

Can fraternal twins be close as identical twins?

If you’re expecting fraternal twins instead of identical twins, you may worry that they’re not as close to each other as they grow up.

Well, any type of twin can be as close as any other type of sibling ‒ it’s down to the individual children.

After all, even though they’re twins, they’re still separate people ‒ individuals to themselves.

Do twins feel each other’s pain?

Technically, no, identical or fraternal twins can’t feel each other’s pain, or read each others’ minds.

But as they grow up together, they may have high empathy for the other twin, so they may sympathetically feel their emotional and physical pain, but there’s no scientific proof to suggest a supernatural connection.

Do twins have a bond?

Yes, twins do share a special bond ‒ they’re siblings, but they’re the same age, and will experience some of the same key moments at the same time.

By sharing a birthday and a sibling connection, the bond between identical or fraternal twins is something truly beautiful.

Identical vs fraternal twins FAQs

So now you know a little more about the differences between identical vs fraternal twins, let’s explore some other t-winning questions you might have.

Can twins have two different fathers?

They certainly can ‒ it’s very rare, but you can have twins with different fathers, called superfecundation.

Can twins be conceived on different days?

Yes, fraternal twins (or even superfecundation and superfetation twins) can be conceived on different days ‒ again, it’s very rare, but it does happen.

What are twins born on different days called?

It depends on what type of twins they are ‒ you can have any type of twins born on different days.

For example, one identical twin could be born late one evening, and their sibling could arrive soon after, but in the early morning of the next day.

Can twins have different blood types?

Identical twins will have the same blood type, but fraternal twins may have different blood types or the same blood type.

Are identical twins 100% the same?

Yes and no.

While identical twins do share the same DNA code, there can be other things that influence their individuality.

If, for example, one twin happens to get more nutrients from their umbilical cord than the other, they may be a little bigger than their twin.

Plus, while they may come from the same egg, the way they develop in the womb may be marginally different, resulting in them having small differences between them.

What are polar twins?

Polar twins are a result of an egg being released that splits into two halves, both of which are then fertilized by different sperm.

So polar twins will share the same chromosomes from their birthing parent, but different chromosomes from their non-birthing parent.

Can I have twins if my husband is a twin?

Actually, the gene for twin prevalence is only passed down from the birthing parent’s side.

So if your husband is a twin, and your family doesn’t have twins, your chances of having twins won’t be increased.

But if you’re a twin or you have a family history of twins, and you’re the one getting pregnant, the chances of having twins is increased significantly.

What are super twins?

“Super twins” sounds like a crime-fighting duo of caped crusaders, but it’s actually another term for superfetation twins.

This is when you get pregnant while already pregnant.

But if you’re worried about having sex while pregnant and having super twins, don’t fret, mama ‒ the chances of this happening are very slim.

Can IVF cause identical twins?

As rare as it comes, actually yes!

During the embryo transfer process in IVF, if you opt for a double embryo transfer, the chance of fraternal twins is high.

But the chances of identical twins in IVF is about 1.2% to 8.9%.

So, there you have it!

All there is to know about identical vs fraternal twins!

If there’s anything else you want to know about preparing for double trouble, there’s always a Peanut mama (or two, or three) that’s happy to help.