Twin tests or ‘Twin Zygosity’ tests can determine whether twins are identical or non-identical (aka fraternal) twins.
Identical twins are where one sperm fertilises one egg and that fertilised egg divides in two to produce two identical embryos. Non-identical twins are where two separate eggs are fertilised by two different sperm at the same time, and two non-identical embryos are created.
Some providers can even detect ‘semi-identical’ twins where two sperm fertilise one egg, but these cases are extremely rare.
On purchasing, the provider will send you a testing kit with everything you need to take the samples. You can take the samples at home and after you send the kit back, they’ll be in touch with the results a few days later. You can choose how you are contacted, with email generally being the quickest service. Some providers offer express services but these often come with extra fees.
Look out for companies selling cheap kits. That’s exactly what they are – just the kit and no testing. Providers then charge more to actually run the test when you return the samples.
Isn’t it obvious when twins are identical?
Not always, because environmental factors can cause identical twins to appear different to each other, and non-identical twins can still look extremely similar.
For some twins, understanding whether they’re genetically identical or have each inherited unique characteristics from their parents is very important.
’Peace of mind’ or ‘legal’ test?
There are two types of twin test: ‘Peace of mind’ tests and ‘legal’ tests – legal tests are court admissible. The science behind the tests is exactly the same – the difference is that for court admissible tests, somebody official needs to watch them being taken so the court is assured that the samples came from the right people. Court admissible tests also require that the samples be handled securely all the way to the lab.
Are the tests accurate?
Yes, because it’s simple for a provider to compare both sets of DNA and confirm whether two twins are genetically identical or dissimilar.
Watch out for shipping fees added at the checkout. Some providers with offices in the US will use labs overseas, so if having your samples tested in the US is important to you (and the provider’s website isn’t clear) check out our listings for these details.