Does everyone tell you your fraternal twins look identical? They might be! We did a twin zygosity DNA test to learn whether or not our twins were fraternal or identical. Here are the results!
When we found out we were pregnant with twins, our doctor told us they were fraternal. They had two separate sacs and two separate placentas — no medical mystery here. We assumed that was correct and just went with it.
When the boys were born, we thought they looked quite different, and it was generally easy for us to tell them apart. It probably also helped that for three and a half weeks they were in their own NICU pods (they were born early at 32+5 weeks). But Sebastian weighed nearly a pound more than Callum, their faces were shaped differently, and the shape of their ears was quite different as well.
But as they got older, we realized that they only looked different to people who knew them well — close family and friends who saw them often. Most strangers would say, “Oh! Identical twins! How fun!” And I’d have to do the song and dance about how they were actually fraternal and use the word “placenta” too many times for a conversation with a stranger. Even Ryan and I would mix them up sometimes, and it would always throw us off.
So we wondered: can fraternal twins actually be identical?
Fraternal twins who end up being identical is a small, often-debated percentage — between 3% and 20% usually. Here’s how it happens. (This is a basic lesson in twins — there are actually seven types of twins but I’ll leave it to the professionals to explain them all).
Fraternal twins are the result of two eggs being fertilized by two sperm. The zygotes implant separately, meaning each baby ends up developing their own sac and placenta. Fraternal twins can be boy/boy, boy/girl, or girl/girl.
Identical twins are the result of one fertilized egg splitting. The split usually happens around days 4 or 5, after the placenta and sac have started forming. Which means the two babies end up in the same sac, sharing the same placenta. Identical twins are always boy/boy or girl/girl.
But if that egg split happens on days 2 or 3, before the sac has started to form, each zygote develops its own sac and placenta. What looks like fraternal twins to medical professionals is actually identical twins!
The only way to figure this out for sure is to do a DNA test. Fraternal twins will have similar DNA like in regular siblings, whereas identical twins will have identical DNA markers. You can get a test at Easy DNA. They sent us the testing kit and we swabbed each of the boys’ cheeks four times and sent in our samples. The turnaround time was quick and soon we had an envelope in the mail with the test results!
Even after all the times we’ve confused the boys and all the comments from strangers, I was still 90% sure my boys were fraternal. So was Ryan and so was pretty much everyone who spends time with them. An informal poll on Facebook had my friends split about 50/50 whether or not they were identical.
And the result?
Our boys are IDENTICAL!
I am still shocked. I was sure they were going to be fraternal! Their personalities are so different, and I can see so many physical differences between them. But the DNA test doesn’t lie.
This also explains (sort of) a little more on why we had twins at all. Fraternal twins are the type to run in families — but we have no twins anywhere in my family’s line. Identical twins are, well, freaks of nature and don’t run. Having this weird miracle somehow makes a little more sense to me than having fraternal twins.
Are you a twin mom? Have you had your twins tested? I’m curious to see what your results are!
Comments & Reviews
Diana Dooley says
My twin and I are 58 years old. Always believed we were fraternal because there was two placentas. My daughter did a DNA test on a site I was not on, but my twin was. It linked my daughter with my sister being her parent. So my sister and I did a DNA test and it came back as identical. We always assumed one sack identical two sacks fraternal. They didn’t have all the testing they have now when we were born. Not that it really changes anything but then again it does :-) we don’t look exactly alike but like your boys, strangers always thought we looked just alike. we sound just alike same hair color same eye color same build. We have always been extremely close and I feel like this explains a lot . Thanks for your article it was very informative.
Tracy says
My sister and I were always told we are fraternal. In about 3 mins (had to wait 30 mins after drinking) I will do my DNA swab. I will send it off today and I cannot await the results. We are apart of the MATR (Mid-Atlantic Twin Registry). I didn’t even know we could do this DNA test to find out. We are 43 and this is our b-day present to each other. April 9th. In 1977 the Dr told my mom we were fraternal. I hope (my sis does too) we are identical. I will find out in a couple weeks! So excited!
Cori George says
That is SO exciting Tracy! Let me know what you find out!!
Linda W. says
We gave our adult children, a daughter and twin sons 23andMe kits this last Christmas. We Just found out that our sons are actually IDENTICAL twins. For 38 years we thought they were fraternal twins who just looked a lot alike! They looked different at birth and weighed a pound apart. By the time they were a couple months old they did look a bit more alike but we still always thought that they were “close but not identical” and would always have to explain that to new people. Even both of their wives thought they were identical! I am still coming to terms with it. I keep going back to look at old photos with a new perspective now…. It’s so funny!
Cheryl Garland says
My twin sister and I are 51 years old and always were told we were fraternal only to find out we are identical after doing DNA testing over the holidays. Our story is much like the other ones in the comments. We’re still trying to wrap our heads around it. Too bad both of our parents have already passed on. They’d get a kick out of this.
Elise says
How fun! My mother was told my twin sister and I were fraternal (two sacs) at birth and never questioned the doctor. My twin sister and I spent our first 30 years believing we were fraternal until we decided to take a genetic test for our 31st! Come to find out we are identical and it has simultaneously changed nothing and everything! As individuals respectively fascinated by nature/nurture/human development, this “new” information/reality has been interesting and fun to digest…we are currently raising our respective families in two separate states…and my husband and I have decided to move closer to my twin sister next year – sometimes I wonder if the dna testing affirmed/strengthened our connection and desire to be close and raise our families together. On a fun side note, we each have toddlers, only 4 months apart – and they definitely look like siblings/fraternal twins! We celebrated our 30th birthday by participating in the twins festival in Twinsburg as fraternal twins – we are thinking about returning for our 35th and wondering what/if anything will feel different returning as identical twins! It’s fun to hear I/we aren’t alone in this discovery process!
Vickie bartlett says
My twins were born 37 years ago and i was told non identical, school friends couldn’t tell them apart, their own father couldn’t tell them apart, I also struggled at times. They would go into each others classes at secondary school and never got caught, this year they had a DNA test and yes they are identical as I always thought they were, have sent for my maternity notes to find out what made the Dr tell me fraternal.
Cori George says
That’s awesome Vickie! Your Dr. told you they were fraternal because they were in separate sacs—every sign points to fraternal when there are two sacs. That’s why the only way to find out for sure is a DNA test. :)
Dionna Hayden says
THANK YOU for making this clear to me! For years, I’ve pondered why my girls looked freakishly alike and have those crazy “twin-powers” identicals usually have. I’m also tired of explaining that my girls are fraternal and the whole identical side bar mystery. We will be getting our test soon and the 13 year old mystery will be finally solved LOL!
Cori George says
That is so exciting Dionna! I’d love to know what you find out! :)
Robin says
I’m so glad you wrote this!!!! We have the a similar story up until the test part. We have not done the test yet. We were always told fraternal, but the placenta was fused when it came out and I thought their head shapes and eyes were different, weight and height is different too (an inch diff and 6 oz). I’ve always been able to tell them apart as well as my husband and son, But everyone else is always questioning or asking if they are identical. They are girls and same blood type too. Their hair is the same, just different hair parts on opposite sides of their head and they each have an elf ear on opposites of their head. So everyone brings up mirror twins! Anyway, I will do the test! You just explained everything so well. I’ll let you know results if I remember to!
Cori George says
I’m excited to hear your results!!
Sarah says
I am an identical twin. I found out at the age of 29. I like to at first tell people I found out I had an identical twin at almost 30, cause of people’s reactions. Then I add the “well, I already knew she was my twin, but we were told that we are fraternal.” The weird thing is that our entire life we always said we felt like we were identical. It was almost as if we knew with every fiber of our beings we were one. My mother was so confident that we looked nothing alike, at least not more similar than her other singlets looked alike. On top of that she also felt sure that she knew when we were individually conceived. Being a biologist, I was really curious about my dna. This was when all the cheap genetic testing was gaining some popularity. A few members of my family did 23andme, including my sister and I. When the results came back it said I had an identical twin. We were members at a health club that was half spa type area/gym and the other half was all of your doctors, nutritionists, etc. on the other half. They had a geneticist on staff that did health related testing. It has a tiered membership, so having the doctor service was insanely expensive. Despite not being elite members, she was willing to test us again to verify. Sure enough, we were confirmed identical. Not only that, even the slight variations between identical twins gene expressions were fewer than average. I think it happens more than suspected.
Cori George says
That’s an amazing story! I love hearing people’s experiences finding out they are identical twins :)
Fabian says
“It was almost as if we knew with every fiber of our beings we were one”
As an identical twin myself, this sentence made me cringe. I’ve always hated not having a true unique identity of my own. I just cannot fathom how people like being seen as ‘one’.
I wouldn’t wish it upon my worst enemy to be an identical twin.