What Are Mirror Image Twins?

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what are mirror image twins

Mirror image twins is a term used to describe identical twins who’s features are exact reflections of each other. Certain physical characteristics are on opposite sides.

For example, if one twin has a birthmark on the left side of their body, their twin will have it on the right side. I find mirror twins to be absolutely fascinating (spoiler alert- probably because my identical twin girls are mirror image twins!) and I’ll get into the details of mirror image twins below.

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When our twins were born, we had no idea if they were identical or fraternal.

Since they are di di twins (each twin had their own amniotic sac and placenta), and are both girls, they could be either.

The only way to know for sure with di di twins is to do a DNA test. Since they were in the NICU after they were born, it wasn’t a high priority for us to find out if they were identical or fraternal right away.

There was a weight difference of almost a pound, so it made it pretty easy to tell the girls apart. Other than the weight difference though…they looked VERY similar.

My husband and I would visit them in the NICU and just stare at their little faces in awe. They looked so much alike!

However, since they were di di twins, the likelihood of them being fraternal was higher than identical. Fraternal twins can look similar and identical twins can look different.

Even though identical twins have literally the exact same DNA, their physical features are affected by the environment, including how they are positioned in the womb.

Early in their NICU, we had a visit by a pediatric ophthalmologist, because they had what looked like birthmarks inside their pupil. They described them to us as cloudy starbursts inside their pupil.

The really crazy thing was that they were on opposite sides. Since this was something they were born with and it wasn’t identical, I figured they were probably fraternal.

It was my mom who first mentioned that they might be mirror image twins and I started researching about the different types of twins.

It turns out that marks in their eyes were actually cataracts and nothing to worry about. Since they’ve come home from the NICU we’ve had to have follow-up appointments with the pediatric ophthalmologist to monitor their cataracts, but so far they aren’t interfering with their vision.

Mirror Image Twins Are a Type of Identical Twin

We finally got a DNA test done after a year and found out that Josie and Margo are indeed identical twins. With this information, and based on their physical appearance, they are mirror image twins.

Characteristics of Mirror Image Twins

As I mentioned earlier, mirror image twins are exact reflections of each other.

Features that can be on opposite sides include:

• hair parts and whorls
• birthmarks, freckles
• tooth eruption
• eye conditions
• eye shape
• right-handed vs left-handed
• ear shape
• dimples
• in extreme cases of mirror imaging, internal organs
• twirl in opposite directions

Related: Children’s Books About Twins

Is There a Test for Mirror Image Twins?

No, there is no DNA test to determine if your twins are mirror image. It is simply based on observation.

Mirror Twins Percentage

Since there is no DNA test to conclude if twins are actually mirror image or not, there isn’t an exact way to know what percentage of twins are mirror image. I’ve read in a few places that 25% of identical twins are mirror image

What Causes Mirror Imagine?

There are a few speculations as to what causes mirror imaging, but I’m convinced that we don’t know the answer yet. There seem to be many things about twins that we don’t know the answer to!

Someone needs to do some more twin research so that I can know! Here are the possible causes that I’ve read over.

Twin Pregnancy: Everything You Need to Know

When the Fertilized Egg Splits

A common consensus is that mirror imaging occurs when the twins split from one fertilised egg between 7-12 days after conception. This would make sense, except for the fact that my twins, who definitely mirror image qualities, are di di twins, meaning that they split within days 1-3.

I’ll break it down for you:

Di/Di twins (separate sac and placenta) egg splits between days 1-3 <— my girls

Mo/Di twins (separate sacs, shared placenta) egg splits between days 4-8

Mo/Mo twins (shared sac and placenta) egg splits between days 9-12 <– what supposedly causes mirror image twins

Facing Each Other In the Womb

A Huff Post article states that twins become mirror images of each other when they are facing in the womb. This just doesn’t make logical sense to me, and my girls weren’t facing in the womb.

My Experience With Mirror Image Twins

The most fun part of my post, where I get to tell you all of the cool things that I’ve observed with my girls! Pictures show it the best, so I’ll share a few as well.

Eyes

They have cataracts in opposite eyes… but there’s more, too. They each have one strong eye and one weak eye. The first time they went to their eye doctor, he literally said that their eyesight is mirrored.

Hair

Their hair parts in opposite directions. This was hard to tell at first because they didn’t really have enough hair. Once their bangs grew out, it was very apparent.

Teeth

As babies, their teeth always came in at the same time, but on opposite sides.

Hands

I’m not entirely sure if they’re right or left handed (2nd/3rd child problems), but they suck opposite thumbs.

Behavior

One of the funniest things I’ve noticed about their mirrored behavior is when the girls role up their pant legs. They sometimes do it when they wake up from their nap, and will each roll up the opposite leg as their sister.

Super interesting if you ask me!

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