If you are a twin or a parent of twins, you have probably heard this question a countless number of times. The next question that often follows is, “are you identical or fraternal?” Different gendered twins are no doubt fraternal, but twins of the same gender can be a fraternal or identical mystery without even realizing it. Complicated deliveries, tricky timing, and human error can all muddle the waters on whether twins are identical or not. Here we detail one advancement in DNA testing: the twin zygosity test.

Twin Zygosity

The twin zygosity test formally determines whether a set of twins, triplets, or multiples are identical or fraternal. Zygosity refers to whether twins are of the same zygote, or egg, which determines if they are identical or not. Repeating DNA sequences are examined, and if several of the repeating sequences are the same when compared to the other twin’s DNA, it is 99% likely that the two are identical. The same process is repeated for triplets or other multiples.

Surprisingly, 25-33% of same gendered twins identified as fraternal are in truth identical. This mistake is a common pitfall when each baby is in their own amniotic sac, as the presence of separate amniotic sacs is most common with fraternal twins. Many other factors complicate identifying identical and fraternal twins correctly, but officially knowing identical and fraternal status can be helpful in many ways. This is especially so if one twin needs an organ donation or develops a genetic illness – knowing the compatibility of their organs or the potential that a twin will develop the same illness is one huge advantage of twin zygosity testing.

After twin zygosity testing, you can answer that question with certainty once and for all – call us today at (800) 219-4362 to begin the quick and simple process!