Twins DNA Testing: Identical or Fraternal?

Mar 27, 2018 | Blog, DNA test



Are Your Twins Identical or Fraternal?

Without a doubt, this is a question all parents of look-alike twins get every time they break out the double-stroller, pack up the extra-large diaper bag, and go out into the world. If your parenting life is double-the-fun, you may think you already know the answer to that question. But do you really? In a nutshell, unless an ultrasound showed that your babies shared a single amniotic sac, only twins DNA testing can tell you for sure whether they’re identical or fraternal.

Basic Types of Twins: A (Very) Quick Primer

Before the widespread use of DNA testing, medical professionals (and therefore parents) assumed that, if twins had their own amniotic sacs and their own placentas, then they must be fraternal. Not so fast!

Fraternal twins come from two eggs being fertilized by two sperm. The zygotes implant separately, have their own in-utero “condos,” and can be girl/girl, boy/boy, or boy/girl.

Identical twins come from a single fertilized egg that splits in two. This division happens usually around days 4 or 5, and after the placenta and amniotic sac have started developing.


If the fertilized egg splits before the placenta and amniotic sac normally start forming for identical twins, say around days 2 or 3, then each zygote develops its own sac and placenta.

So what could look like fraternal twins to medical pros is actually a set of identical twins!


Twins DNA Testing_3_Argon and Aldridge

Twins DNA Testing: Argon & Aldridge

We recently did twins DNA testing (Twin Zygosity Test) for two very handsome young men from Idaho named Argon and Aldridge, who were born in January, 2018. They are Dichorionic Diamniotic (Di/Di) twins, which means each of them had their own amniotic and chorionic sacs. Although the majority of twins of this type (70 %+) are fraternal, the boys’ parents wanted to confirm their relationship—and the only sure way to do that is with twins DNA testing.

Their mother, Ally, who writes a lovely parenting blog, told DDC: “It doesn’t really matter to us if they’re identical or not. Yes, we’re curious, but I think the boys would eventually want to know if they’re identical or not.”

Twins DNA testing_3

How It Works

  1. DDC sends DNA-collection materials, swabs, and directions to test participants (or to their parents, if they are minors)
  2. Buccal (cheek) swabs are used to collect the DNA from each participant. It’s non-invasive, fast, and pain-free
  3. The customer mail samples back to the lab where they are tested and analyzed by our team of PhDs. And in just a few days, the report is posted to a secure online account for viewing

A probability of relationship is given for twins DNA testing, just as it is for paternity-test results, except in this case the probability is for whether the twins are identical or fraternal.

Want to know what Argon’s and Aldridge’s test results were? Check out the video above!

Facts about Twins

Here are some quick, fun, facts about twins:

  • 1 in 90 live births are twins
  • If you are a fraternal twin, you have a 1 in 17 chance of having twins yourself; but if you’re an identical twin, your chances of having twins are the same as for non-twins
  • One-third of all twins born in the U.S. are identical
  • The average birthweight for a twin is 5 lbs 5 oz
  • Children of identical twins are genetically half siblings
  • If identical twins were to marry other identical twins, their children would technically be cousins, but their DNA relationship would be that of full siblings

Final Thoughts about Twins DNA Testing

With today’s advances in DNA science, there is absolutely no good reason to wonder whether or not twins are identical or fraternal. As they get older and their brotherly bond deepens, Argon and Aldridge will be thankful that their parents had this test done on their behalf.
Thanks to Argon and Aldridge’s parents and siblings for agreeing to share their story. Follow them on Instagram: @theblackandwhiteblogco


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