The Results Are In

Turns out, our twins are identical. Huh.

Since the day we discovered I was pregnant with two, every medical professional told us that our twins were fraternal. I believe the “there’s two in there!”ultrasound tech  immediately told us they were fraternal, but I was in shock so I don’t remember. Then my OB said there was a 99% chance they were fraternal. Later, our pediatrician, who we love, also said that our type of twins (known as “di di twins”) is “textbook fraternal.”

Our girls are diamniotic/dichorionic (aka “di di”) twins, which means they were in their own sacs and had their own placentas. It’s a common misconception that di di twins are always fraternal; however, the only way to rule out identical twins (that are the same sex and have the same blood types) is to do a DNA test. Identical twins can look different and fraternal twins can look alike. It is not possible to say with 100% certainty that same-sex twins are fraternal just by looking at them (but, honestly, if they look really different, they’re probably fraternal). Boy/girl twins cannot be identical…because one is a boy and one is a girl – no DNA test required there.

Right after we got home from that first ultrasound appointment, we started researching di di twins. We’ve suspected since that first Google sesh that there was more than a 1% chance our twins were identical. After our girls were born, we found out they had the same blood type, but we still didn’t get a DNA test right away. After wondering aloud for almost 2 years, we finally ordered a home DNA test. How cool is it that you can get your DNA tested for 100 bucks nowadays? Science!

After we got their results (the likelihood they’re identical is 107,987,712,983 to 1), I immediately started researching. I wanted to find out how common it is for di di twins to be identical.  To my surprise, I couldn’t find much good information. A Google search for “di di identical twins” returns a few articles, but mostly blog posts and forums. Blogs and first-person accounts are only good in an anecdotal sense. A search for monozygosity1 on Amazon returns a single book that is “currently unavailable.” It boggles my mind that it’s 2017 and I can’t find what I need on online. When’s the last time you Googled something and couldn’t find a single suitable result?  I even tried our local library! Although it’s a good library, it only has a couple of twin parenting books, and otherwise carries almost exclusively fiction on the topic of twins (i.e. The Midnight Twins or The Templeton Twins Have an Idea). All I want is a few scientific articles or a book written by a perinatologist or anything other than Sally K.’s personal experience with her di di twins turning out identical.

After some more poking around, the following link is the best, seemingly legit summary of twin facts I have found so far:

Why does all this matter? It really doesn’t, except that people ask me on a daily basis. As the twins grow up, I’m sure people will ask me less, but I imagine the twins will have to answer the “identical or fraternal?” question for the rest of their lives. It doesn’t bother me at all to field twin questions because I am still fascinated by the whole thing, too. What bothers me is the widespread misinformation that almost everyone has heard, and that even doctors seem to believe it. It would also be cool if our local library carried something other than tacky twin murder mysteries.

I would have bet money they were fraternal, so I’m glad I didn’t do that. According to my identical/fraternal Facebook poll, 59% of voters also agreed with me. So it looks like our twins have managed to surprise us again. I guess twins are funny like that.


1 Monozygotic = one egg (identical twins); Dizygotic = two eggs (non-identical a.k.a. fraternal)