Twin DNA – the science behind one of our most popular tests

Twin DNA – the science behind one of our most popular tests

As a leading DNA testing laboratory, we are often asked about the science behind peace of mind DNA testing, especially when we’re talking about twins.

In the US, around 3% of pregnancies results in a multiple birth: a trend that has risen significantly in recent years and can be attributed to fertility treatments like in vitro fertilization (IVF), among other factors.

In this article, we look at the science behind twin DNA (zygosity) testing, how the test is performed, and when you might want to order a Twins DNA Test.

What is a twin DNA test?

A twin DNA test – also called a zygosity test – is a DNA test that can be used to determine whether multiple children from the same birth (twins, triplets, quadruplets etc.) are identical or non-identical.

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If siblings are identical, they are known as monozygotic. This means that they were formed from a single fertilized egg, which went on to split into separate embryos.

Monozygotic (identical) twins share the same DNA profile, physical features, and sex (gender).

If siblings (twins) are non-identical, this is known as dizygotic (i.e. having two zygotes) or fraternal twins.

This means that these siblings are the result of separate fertilized eggs and, although they do not have the same DNA profile, they will share DNA in common (as is the case for siblings from different births).

How is a twin DNA test performed?

An AlphaBiolabs Twins DNA Test (zygosity test) is performed using the very latest technology and techniques in DNA analysis, to determine whether siblings from multiple births are identical or non-identical.

The test requires a cheek (buccal) swab to be rubbed quickly and painlessly on the inside of each sibling’s cheek to collect cheek cell DNA. This simple, non-invasive method of sample collection can be done at home.

Once the DNA samples arrive at the laboratory, our expert geneticists compare both samples, analyzing up to 42 DNA markers (loci) to identify matching DNA markers.

If the siblings are identical (monozygotic) they will share the same DNA profile. If they are non-identical (dizygotic or fraternal twins), they will have different DNA profiles, but they will still share DNA in common, like siblings from different births.

Difference between identical and fraternal twins

Once we have completed the Twins DNA Test, a zygosity certificate is issued confirming the results. This can make a unique gift for multiple birth parents, who want to confirm whether their children are identical or non-identical.

When is a twin DNA test useful?

There are many reasons why you might want to order a Twins DNA Test.

Examples include:

  • It wasn’t clear during pregnancy (in utero) whether the twins were identical or non-identical. Identical twins do not always share the same placenta and sac – it all depends on when the egg splits
  • You want to assess the likelihood of conceiving twins again
  • One sibling has been affected by an illness, and you want to know whether you need to test the other sibling for the same condition
  • You need the information to take part in a study about multiple births
  • You want to buy a Twin DNA Test as a gift for multiple birth parents or their children

Knowing whether twins are identical or non-identical can also be useful for reinforcing the need to treat siblings as individuals.

Where can I buy a twin DNA test?

It’s easy to buy an AlphaBiolabs Twins DNA Test online now from our award-winning, accredited laboratory.

For just $109 you’ll receive your secure, password-protected results via email in 3-5 days after we have received your DNA samples.

Got questions about our Twins DNA Test? Email our friendly, knowledgeable Customer Services team at

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Order your peace of mind Twins DNA Test online now, direct from our accredited laboratory.

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