The Zygosity Test

I know Dave is sick of me telling this (what seems like) 15 minute story to strangers...
Stranger on the street/ in store etc.: "Oh look! How Cute! Twins? Are they twins? Well, of course they must be... are they identical?"


Dani: "We are pretty sure they are fraternal... they were in separate sacs etc. etc.; but we still don't know for sure. A lot of people think they are identical, including our pediatrician. But, we can tell them apart so they are probably fraternal; and, fraternal twins are a lot more common, so it's likely that they indeed are. On the other hand, all of the fraternal twins I have met look quite a bit different... and really, our girls don't except for their size... Stella always being a bit smaller; so maybe when she catches up we won't be able to tell them apart! But once again, we really don't know...


If someone asks Dave: "Are they identical?"... his response is short and to the point: "No, they are fraternal."


So, there are tests for these things.... and to alleviate some of Dave's pain in listening to my same spiel every single time someone asks this question, I decided to get a DNA test done as part of his birthday present.

So while us girls were still in Minnesota, I received the swab kit. I took 8 inner-cheek swabs on both the girls and sent it in for analysis. The company I used specializes in zygosity testing (determining whether twins are mono-zygotic or di-zygotic, or in other words, identical or fraternal).

I was looking up some stats on how common the two types of twins are and I found almost 70% of all twins are fraternal and the rest identical. Even though there has been an increase in fraternal twins due to fertility treatments, identical twins have remained constant.

So there are twins in Dave's family (and some in mine, but far removed) so I am thinking... ok, it's in the family, right? I learned that having fraternal twins can be partially attributed to heredity; I also found out that, despite popular belief, identical twins are not hereditary. With these facts, I was even more convinced that Dave was right all along and they are definitely fraternal.

The results came in a few weeks later.

After the analysis of a quantity of highly-variant DNA markers from the swabs of both girls, it was determined with over 99% probability that Lucy and Stella are mono-zygotic twins.

So guess what?
As it turns out, we do indeed have identical twins!