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Twin Zygosity Testing

Twin zygosity testing is a type of DNA testing that determines if twins are identical or fraternal - monozygotic or dizygotic. It is a simple and painless procedure that usually costs less than a hundred bucks.

So, let's talk about how and why it's done...

How Twin DNA Collection is Done

If you would like to have this test done, you must first order a Twin Zygosity Test Kit. Kits are available through several reputable companies on the web which allow you to purchase online, by mail, or over the phone for added convenience. The test will be mailed to you and will include two separate collection swabs and envelopes (one for each twin). Detailed, easy-to-follow instructions will also be included.

Basically, you use the swab inside the mouth on the inner cheek to collect cell samples. This is completely painless and very easy to do (I am speaking from personal experience with my own twins!). When finished, the swab is then placed inside an envelope labeled with that particular twin's name.

When the process is completed with both twins, the package will need to be sent back to the testing company for analysis. A box or envelope in which to dispatch the samples is usually included in the kit.

As far as when to expect results, each company will be a little different. Generally, results can be obtained within a couple of weeks. However, with advancements in technology, it's sometimes only a couple of days.  That's especially helpful for those parents that just can't stand the anticipation!

Additionally, there may be a few different options on how you receive the results. Most will offer result reports via e-mail, over the phone, or directly through the mail.

Why Bother With Twin Zygosity Testing?

Twin DNA testing is done for different reasons. Mainly, parents just want to know. But, because identical twins share the same DNA, it is a good thing to be sure of for health issues that may arise. For example, both twins may be susceptible to the same diseases.

Due to the constant questions parents get about their twins being either "identical" or "fraternal", many of the unsure will resort to zygosity testing for a definite answer to give family, friends, and those pesky strangers.

And, of course, there are those who pursue a DNA test out of pure curiosity. In any case, with the technology we have today, these tests are more than 99.9% accurate. That should put to rest any questions!

Testing for zygosity is recommended for all same sex, same blood type twin pairs. Examination of placentation is not always reliable, as in this study from the American Journal of Obstetrics and Gynecology where zygosity could not be determined in about 35% of twins by clinical or pathologic assessment at delivery.

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