DNA Testing for Twins
Updated on March 18, 2024
Back to top
back to top icon
DNA Testing
DNA Testing for Twins

A DNA test can prove that two people are related and the degree to which they are related. To prove that two people are twins, they’d need to undergo a twin zygosity DNA test.

DNA stands for deoxyribonucleic acid. It carries genetic information, which is something each person shares with their ancestors.

DNA shows a link between more distant relatives, including:

  • Cousins
  • Grandparents and grandchildren
  • Aunts and uncles and nieces and nephews
  • Siblings
DNA Testing for Twins 6

Source: 123rf

Are DNA test results different if siblings are twins?

It depends on whether they are fraternal twins or identical twins.

Identical Twins

Identical twins or monozygotic twins are two different people who grew from a single fertilized egg and one sperm.

Once the sperm reaches the egg, the fertilized egg splits into two identical cells, which eventually manifest in the same physical characteristics and nearly genetically identical people. As monozygotic twins grow, they are an exact match of one another and share the same DNA.1

This means that their genetic signature is almost if not an exact match. This is commonly observed in many DNA tests that cannot tell identical twins apart.2

Take note, however, that recent studies have also shown that the 99.9% figure can also fluctuate slightly (around an average of 5.2 mutations can distinguish them), given some possible genetic mutations the eggs go through.6

Fraternal Twins

Fraternal twins, or dizygotic twins, are two separate eggs fertilized by two separate sperm. They are not identical, and aside from being in utero and born at the same time, they are biologically no closer than any other siblings.5

If twins are identical twins, DNA will show this. Identical twins’ DNA profiles are identical. They look the same, they are the same sex, and they have the same DNA.

If they are fraternal or non-identical twins, their DNA sample will show only that they are siblings. Fraternal twins’ DNA profiles are very similar—approximately 50%, although this figure fluctuates—but no more similar than siblings born separately.5

Not only can a twin DNA test help you determine your twin relationship, but it can also help an expectant mother determine if her twins are fraternal or identical while she is pregnant.

How Do Fraternal Twins Happen?

Sometimes, a woman releases two eggs instead of one, and both are fertilized. This means that different combinations of DNA occur when the cells start to multiply, leading to non-identical twins.

Know Your DNA Reviews

Best DNA Kit

Don't miss out on the opportunity to learn more about yourself. Read our best DNA test page to find the best one for you.

Can a DNA Test Prove Identical Twins?

Yes, you can get a DNA test to see if you’re identical twins.

You can use a DNA profile or a twin zygosity test to determine if you’re identical or fraternal twins.3 This will require comparing the DNA profile of each twin to the other and seeing if they’re an exact match or not. Identical twins often share over 99.9% of their DNA since they grew from the same combination of chromosomes, and the egg split later on to make two copies.4

These tests are relatively accessible and will only take anywhere between five to seven business days (depending on the company; some may take additional business days or even fewer).

How Does Twin DNA Testing Work?

If you or anyone you know wants to undergo twin zygosity testing (whether it’s for health reasons or just out of curiosity), here’s how it works for most companies (some may vary):

  • DNA samples (a mouth swab is common, so is a blood sample) will be collected from both you and your twin
  • Depending on if you do it at home or in a facility, you will either have to ship your twin zygosity test sample, or they’ll take the samples with them—either way, they will be sent to a laboratory for testing
  • Wait for your results (wait time depends on the company or facility)
  • Interpret your results with a trusted healthcare professional or, if the laboratory you had it done in can provide it, a geneticist or specialist trained to explain your results to you

Your results will reveal if you’re identical twins or fraternal twins.

DNA Testing for Twins 7

Source: 123rf

Can You Do a Twin DNA Test At Home?

Yes, you can. Several companies offer at-home twin tests and other relationship tests.

They’ll send you a sample collection kit as well as their own instructions for sending it back, wait time, etc.

However, you need to keep in mind that at-home DNA testing is not considered a “legal test.”

It’s legal to take the test, and it can provide you with information. However, the results are not recognized by the court system. A legal test must be performed by a doctor and/or at a DNA testing clinic for the legal system to officially recognize.

If you’re interested in taking a DNA test for legal reasons, speak to an attorney or contact the court to determine what constitutes a legal test in your situation.

How Much Does a Twin DNA Test Cost?

It depends on the company, but many companies and facilities start pricing at a baseline of $100.

DNA Testing for Twins 8

Can Twins Have Different Fathers?

Yes, but it is extremely rare. And in most cases, nobody will ever know that there are two different fathers.

If two different sperm fertilize two different eggs at approximately the same time, it can result in two babies that appear to be fraternal twins.

DNA testing would show them to be only half-siblings

How Early Can Twins Be Detected?

Twins are detectable very early in a pregnancy, even in the first trimester.

In the case of fraternal twins, there will always be two fertilized eggs, so it will be easy to detect them. When it comes to identical twins, they can’t be detected until the egg splits, but this happens very early in the development process, so it shouldn’t be too much of a surprise.

Twins can be classified as:

  • Di-di (dichorionic diamniotic)
  • Mo-di (monochorionic diamniotic)
  • Mo-mo (monochorionic monoamniotic)

Di-di, mo-di, and mo-mo classifications are not always an indication as to whether twins are identical or fraternal.

DNA Testing for Twins 9

Dichorionic Diamniotic (Di-di) Twins

Di-di twins, which are twins with their own separate inner and outer sacs and placentas, are detectable at week five of the pregnancy. Heartbeats might not be discoverable yet, but the sacs have formed and are visible.

It’s a rare occurrence, but two placentas sometimes fuse into one, which makes it seem as if fraternal twins are identical. A DNA test would prove otherwise.

All fraternal and a third of all identical twins are di-di.

Monochorionic Diamniotic (Mo-di)

Mo-di twins aren’t detectable until after six weeks. These twins share a chorionic sac but different amniotic sacs. There is only one placenta in this type of pregnancy.

Mo-di twins share one placenta and one outer membrane, but each has its own inner membrane. This is the most common type of identical twins.

Mo-di twins are always identical.

Monochorionic Monoamniotic (Mo-mo) Twins

Mo-mo twins also aren’t detectable until after six weeks. These twins share both chorionic and amniotic sacs.

Mo-mo twins share a single placenta and outer and inner membranes. This is a very rare occurrence and accounts for only about one percent of all identical twins.

Mo-mo twins are always identical.

How are After-Birth Twin DNA Tests Performed?

If it is impossible to tell for sure during the pregnancy that twins are identical, DNA testing is performed after birth.

This can be done using a blood sample from the placenta(s) or by swabbing the cheek cells from each baby.

Samples can be taken from the comfort of your own home and sent to a lab for analysis.

DNA Testing for Twins 10

Why Take an Identical Twin DNA Test?

There can be a number of reasons, some of them being curiosity, health reasons, and even looking into possibilities of organ transplant or blood transfusion, among other potential medical emergencies.

Twins can look much alike without being identical, the same as siblings born at different times. Confirming that twins are indeed identical can clear up any simple curiosity or even inform health decisions.

Another reason is so that twins can take part in scientific studies. Twin studies are still being explored, so their voluntary help could further the research. The test shows that the twins originally split from one egg, so identical twins are able to provide information based on their genetics.

Twin studies are very common, but participants must prove they are identical or fraternal before they are admitted into most studies.

Why is It Important to Know If You’re Pregnant with Twins?

It’s important to know if you’re pregnant with twins because they can come with more complications, like:

  • Twin-to-twin transfusion syndrome – Approximately 15% of monochorionic twins experience twin-to-twin transfusion syndrome, in which one twin gets too much blood, and the other does not get enough. Knowing if your twins are identical can help doctors look into this possibility much faster.
  • Too much amniotic fluid – Amniotic fluid can build up more because there is an additional fetus growing, so you may have to watch out for an excess
  • Too little amniotic fluid – On the flip side, your body may not develop enough fluid for both babies
  • Premature labor – Because twins take up more space in the uterus, there may be disruptions to the placenta, which can cause early delivery
  • Anemia – You (the mother) can develop anemia as your body will ensure that more stores of iron will go to the babies before you, and because there is more than one baby, you may not get as much iron in her blood
  • Doubled risk for congenital disorders – Because there are two babies, there is a higher risk that they will inherit genetic disorders
  • More frequent doctor check-ups – In order to manage or identify possible problems, more doctor check-ups are required

Know Your DNA Reviews

The Best DNA Test

Looking for a DNA test that's accurate and can tell you about your health and heritage?

Updated on March 18, 2024
Kelly Brown
Kelly Brown
Content Contributor
Kelly has experience working with clients in a variety of industries, including legal, medical, marketing, and travel. Her goal is to share important information that people can use to make decisions about their health and the health of their loved ones. From choosing the best treatment programs to improving dental and vision health to finding the best method for helping anyone who is struggling with health issues, she hopes to share what she learns through informative content.