Identical vs Fraternal Twins: How to Tell the Different Twin Types

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Identical Vs Fraternal Twins and the Different Twin Types

We are constantly asked if our twin girls are identical or fraternal, usually with about 100 other personal questions.

People are just fascinated with multiple births.  I sometimes don’t mind the questions, and the babies enjoy the attention!

However, other times we are in a hurry, the babies are dangerously close to hangry, and I can see Theo becoming increasingly upset by the attention his sisters are getting.

It sure would be nice to be able to answer with a simple “they’re identical” or “they’re fraternal” and be on our way.

We finally decided to get a DNA test done, and I’ll be sharing the results at the ends of this post.

BUT FIRST.

Don’t scroll down.

Read this.

I’m gonna share with you guys today some information about twins.  Everything I know comes from books that I’ve read.

I’m not pretending to be an expert, so if I got something wrong, don’t call the science police.

There seems to be a lot of confusion regarding identical vs fraternal twins.

The common misconception is that if twins share a sac and placenta they are identical twins, and 2 sacs/placentas = fraternal twins.

THIS IS NOT TRUE.  I even had nurses in the NICU swear to me that they were identical.

Upon finding out that there were indeed two sacs and two placentas, they would remark at how similar they looked for being fraternal twins.

Can identical twins have separate sacs and placentas? Yes. Yes, they absolutely can. There needs to be more widespread information regarding twin births!

I have been asked so many questions, so I am going to just answer some of them right here.

Commonly Asked Questions Regarding Twins

What are non identical twins called? Fraternal twins

How are twins made? Read below 🙂

How are identical twins formed? Read below under identical twins!

Do fraternal twins have the same blood type? The chances are the same as siblings having the same blood type. It’s possible.

Do identical twins have the same blood type? YES, always.

Can fraternal twins be the same gender? Yes, just as siblings can be the same gender.

The Difference Between Identical and Fraternal Twins

The only way to be 100% certain if same-sex twins are identical or fraternal when they are in separate sacs in the womb is to have a twin zygosity test performed. 

My husband and I went back and forth on whether we should get the test or not.

I finally couldn’t take it anymore, and he agreed, so we sent away for a test kit (Proactive Genetics).  We swabbed their cheeks, sent them off, and waited less than two weeks to get our results!

Identical twins can share a sac/placenta.

However, twins can still be identical if they have their own sacs and placentas.

I’m not going to get into all the science here, because… I just don’t feel like it.  I’ll just give you a brief little lesson 😉

Facts About Identical Twins

Many people don’t know how identical twins occur. Identical twins that are conceived from one fertilized egg are called monozygotic twins.

Monozygotic is just a fancy, sciency word that literally means: identical, from the same egg.

• One egg that has split into two
• They CAN share the same amniotic sac and placenta, and if they do, are definitely identical twins.  This is actually the rarest (and dangerous) type of twin pregnancy.  Twins can have separate sacs and placentas and still be identical
• Gender: Always the same sex. ALWAYS. Don’t ask boy/girl twin parents if their twins are identical
• Blood type: always the same
• Cause: Random, and not genetic
• Appearance: Appearance is identical, or extremely similar
• The chance of having identical twins is 3/1000

Fraternal Twins Facts

Fraternal twins are conceived when the woman’s body drops two eggs at the same time. They are called dizygotic twins, meaning nonidentical and from two different eggs.

• Two separate eggs that were both fertilized by two different sperm
• Always have separate sacs
• Gender: usually different, but can be the same
• Blood type: usually different
• Cause: Genetics (maternal side only; if twins run in the dad’s family, it cannot be passed on.  Two eggs have to be released, and no matter how strong a man thinks his sperm is, it cannot force two eggs to drop.  This can only come from the mother.  Sorry, dads!),
• certain infertility drugs, IVF, advanced maternal age during conception
• Appearance: They look as similar or dissimilar as any siblings could look

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Related: What to Put on Your Twin Registry

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Different Types of Twin Pregnancies

Aside from identical and fraternal, there are different types of twins depending on how they are positioned inside the womb.

If you’re having twins, it’s definitely interesting to know about the different types of twins.

A twin pregnancy is also considered high risk, and you can use a due date calculator to figure out when they will arrive- anywhere from 2-8 weeks early.

Dichorionic/Diamniotic

Most commonly known as Di Di twins, they can be either identical or fraternal.

It means that the babies each had a seperate sac and placenta inside the womb and as far as twin pregnancies go, they are the lowest health risk. Josie and Margo were di/di twins.

Monochorionic/Diamniotic

Referred to as Mo Di twins, they share a placenta but each has their own amniotic sac. Mo/Di twins are always identical. They are in the middle when it comes to the risk factor.

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Read –> How to Increase Your Chances of Conceiving Twins

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Monochorionic/Monoamniotic

Monochorionic twins (abbreviated as Mo Mo twins) share both a placenta and amniotic sac. These are the highest risk type of twin pregnancy and are also always identical.

Both Mo/Di and Mo/Mo twins are at risk for twin to twin transfusion syndrome.

Twin transfusion syndrome is when one of the babies is taking all of the nutrients through the placenta, and the other baby is getting none. This is a risk due to a shared placenta.

There are also polar body twins and conjoined twins, which are very rare, especially in the United States.

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Read –> How to Survive a Twin Pregnancy

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Facts on Josie and Margo

• Di/Di- Separate sacs and placentas (likely fraternal)
• Gender: same (either)
• Blood type: same (likely identical)
• Appearance: I definitely thought they were identical when they were younger.  We even mixed them up a few times.  As they grew, their features became more distinct, and I was really torn!  Even Theo can tell them apart now most of the time (either)
• Twins also don’t run in our family, and we didn’t do IVF or use fertility drugs (likely identical)

(You can read about my twin birth story here, how I got them to sleep through the night here, and see their 1-year-old pictures here.)

What do you think??

A DNA test has confirmed that Josie and Margo are identical {mirror image} twins!

Mirror Image Twins??

There is a rare type of identical twins, called mirror image twins.  Mirror image twins are twins that have identical features, on opposite sides, just like looking into a mirror.

There is no official test to determine if twins are mirror image or not, it is just based off of their physical characteristics.

These characteristics could include birthmarks, freckles, teeth, ear shape, cowlicks, hair whorls, etc.

There was so much fascination about mirror image twins that I wrote an entire post that you can find here: Mirror Image Twins Facts. I go into detail about everything I’ve noticed with my girls, as well as lots of pictures.

Josie and Margo have cataracts in opposite eyes, and their teeth have always come in at the same time, yet on opposite sides.

See that little dot in the middle of her right pupil?

That’s her cataract, and Margo has one in the middle of her left pupil.

We have checkups with a pediatric ophthalmologist every few months, but so far, they aren’t causing issues; they’re just like a birthmark!

So there you have it, folks!  I’m so happy that we finally know.  Are you surprised by the results?

P.S. Make sure you’re following me on social media to keep up with our family and all the twin cuteness! I am on Instagram, Facebook, and Pinterest!