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Are My Twins Identical?

The answer isn't always as clear as you might think.

By Dave SmithPublished 5 years ago 3 min read

"Are my twins identical?" It might sound like a simple question to answer, but in reality it's not always easy to tell.

What happens if you have a set of same-gender twins who look similar? There are two possibilities: they could in fact be identical—or—they could simply be non-identical twins who just happen to share similar physical features (as many siblings do). Not even doctors & midwives can be certain in all cases, and it's not always possible to get a definitive answer from an ultrasound scan. Contrary to what some people believe, identical twins don't share identical fingerprints—they are formed randomly in the womb.

This can be distressing for many parents of twins. From the awkwardness of not having an answer when asked by a stranger if your twins are identical, to more serious situations like needing to know if both of your children will be affected by certain genetic diseases.

So what can you do if you're one of the many parents who find themselves in this situation? There are several types of twins and various ways to tell whether or not they are identical.

Let's take a look at them one at a time:

When twins are definitely NOT identical

It might sound stupid but we'll say it anyway—if your twins are different genders then they most definitely are not identical.

Identical twins share the same set of genes & chromosomes, and as such they are always the same gender. If you have one girl and one boy, then you have a set of fraternal (i.e. non-identical) twins.

One a similar note—if your twins are the same gender, but they have very different physical characteristics (such as hair colour, eye colour, skin tone or facial features) then you can be fairly certain that your twins are fraternal. Things like hair & eye colour are inherited genetically, so they will always be the same in a pair of identical twins.

Even though they share a womb and are born at the same time, fraternal twins are no more similar than any other 'normal' pair of siblings.

There are even very rare cases when a pair of twins can have different fathers, making them genetic half siblings!

When twins definitely ARE identical

If your twins shared a placenta during pregnancy, then they are 100% definitely identical.

Note that identical twins don't always share a placenta—sometimes they do and sometimes they don't. It depends at what point in time the egg splits in two. But if you know there was only one placenta present, you can be certain that your twins are identical.

When it's difficult to tell

This leads us to situation number three:

  • Your twins are both the same gender...
  • ...and they look alike...
  • ...and there were two placentas present in the womb.

In this scenario, it's possible that your twins could be identical or fraternal.

How can you get answers?

There's only one way to really know for certain, and that's by having your twin's DNA tested. A DNA twin test (also known as a zygosity test) compares cheek cell samples from both twins. If the testing scientist observes that the twins share 100% of their DNA in common, they are identical. If they only share 50% of their DNA, they are fraternal.

It may sound technical and expensive, but with modern technology a DNA test is actually quite affordable, with most companies charging around £100-150 for a twin test. Everything can be done in the comfort & privacy of your own home.

Instagram personality chantellechamps was one such parent who couldn't figure out if her twin girls were identical or not. She decided to get a test done and posted the results on here Instagram page. It turns out the girls were indeed identical.

Some other interesting facts about twins:

  • Identical twins don't run in families - but fraternal twins do.
  • Twins really do skip a generation. A man can inherit the hyper-ovulation gene from his mother and pass it on to his daughter, making his daughter more likely to give birth to non-identical twins.
  • Twins are more common in certain countries. Women from certain African backgrounds are more likely to have twins compared to the general population (27.9 twins per 1000 births), whereas women from Asian and Latino backgrounds are less likely (around 10 twins per 1000 births)
  • Fraternal twins are more common than identical twins. Around two thirds of all twins are fraternal.
  • Taller women are more likely to give birth to twins. Tall women have higher levels of a protein known as Insulin-like Growth Factor (IGF). The protein is responsible for growing longer bones - it also increases the likelihood of the ovaries releasing more than one egg.

About the Creator

Dave Smith

Science man.

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