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
Lorena Munoz says
About 4 months ago, the conservation about the small possibility that my 22 year old twin girls could in fact be indentiacl and not fraternal came up. Since then, we did the DNA testing, but we haven’t opened the results yet. We are having a reveal party next Saturday during our annual family vacation. I can’t wait to find out!
Steve Spin says
Great post your boys are adorable. My twin brother and I look/act/talk/think identically. It is more than just the twin thing. Our wives think we are nuts. We are inseparable and for most it is hard to believe we are fraternal. Our Mom and Dad say we are fraternal. We never believed it. After doing Ancestry DNA I thought it would be great if they did something like that to determine twin type. I happened to stumble on your site and I immediately texted my brother. I am so excited to take the DNA test. I just hope I am not disappointed with the outcome and If it is good news, how mad will we be that we went 43 years without knowing. Either way we are still twins and that’s all that really matters. Thanks for the post
Lucy Sandford says
Oh, same as us, let us know what you find. We are still coming to terms with the news. It doesn’t change our relationship, but so strange to know we have identical DNA.
Lucy Sandford says
Hi, thanks for this post. I grew up believing I was a non identical twins. We had separate sacs and our placentas were fused. The surgeons opinion was we were non identical and it made sense as there were non identical twins on my Mum’s side. We decided to to the ancestry DNA tests and it said it indicated we were identical. We had never questioned it before. So we did a zygosity test to find out and we are in fact identical. So strange to find out something so important at 35! ???? I think more people should definitely be told of the possibility. I had no idea.
Cori George says
I think it would be crazy to find out at 35 (that’s how old I was when I had my boys!). Twins are SO interesting, especially now that science gives us more insight!
Mindy Howard says
This is off-subject, because I came to this site for for information before my twin girls are officially DNA tested, but your boys are just adorable!! I’m sure you’ve heard it many times, but those sweet faces made me smile!
Cori George says
Aww thank you so much! They make me smile too :)
denise says
I am an adult trying to find out if I am a twin. How do we find out for sure. I was born 3 months after her. She told me that she was premature and stayed in the hospital for 3 months then was adopted. I was born 3 months after her. Who can I contact to find out more information. Her birthday is in november my birthday is in march.
Cori George says
Hi Denise — you can use the same kit mentioned in this post. You each do a swab and send it in and the DNA will tell you if you are twins.
Jimmy says
Okay, so i understand the boy girl scenario; however, can someone explain how two brothers or sisters end up being fraternal? Is the only facter seperate/time elapse between fertilization?
Cori George says
It’s the same thing as boy-girl. The eggs are fertilized by either two boy sperm or two girl sperm. Hope that helps!
Jess says
To be fraternal, two separate eggs are fertilised by two individual sperm, creating two babies with their own, unique, genetic makeup. This makes fraternal twins no more similar than regular siblings born at different times and any combination of sexes is possible.
My husband and his twin brother were always told that they were fraternal because they had separate placentas…despite regularly confusing people, including their own family. They were born naturally, only 10 minutes apart and even weighed the same 6 pounds and only 1/2cm difference in length. Their mother colour coded everything, clothes, shoes, bags, bedding etc. just to tell them apart. To this day my husband cannot stand to wear anything blue because “that’s my brother’s!” As teens and young adults they remained very similar and always close together(I was always asked which one I was with). It was not until women, marriage and fatherhood entered their lives that differences began to appear…my husband got two visible moles on the left side of his neck…possibly an influence of environment. I’m thinking of sponsoring a DNA test for their 40th birthdays.
Georgia says
I’m a girl who was born with a brother. We looked identical if boy and girl twins could be and people always made a scene over how we looked exactly the same just boy girl versions of each other. We also got sick at the same time for the same amount of time we were telepathic and as close as we could possibly be. I lost him 2 years ago but I remember when a situation came up that my brothers DNA was searched from some hospital thing and our DNA was the same other than his male and my female DNA we were told it’s likely if either of us needed a transplant the one who doesn’t need one would most likely be a donor match and we were lucky. We had the same everything pretty much and I wish he was still around to explore our similarities more. As babies our parents would sometimes mistake me for my brother and have a moment of confusion as to where my genitals were. It was nice having a boy version of myself.
Megan says
We were told our girls were fraternal at 14 weeks when I had my first ultrasound to confirm multiples. 2 placental and sacs. Of course, the Dr did tell us to test to be sure. They will be 13 next month and I just ordered the kit last night to find out for sure. We never really cared but they’ve been wondering more and more lately. I think they’re hoping they’ve been arguing the right side all these years! Haha! Almost no one can tell them apart except very close family and friends. I’ve seen enough parents sure one way or the other proven wrong by science to try and make a guess. I just hope they’re happy with whatever result they get ;) either way, it’s pretty cool there’s a way to know for sure. My girls say if they’re fraternal they don’t want kids bc they don’t want twins. Hahaha!
ann says
This is fascinating! I am a twin, supposedly fraternal but we have always had our doubts about that. My mother has long suspected that we are mirror -reverse. As babies and children we looked identical. We look less alike now , but I attribute that to lifestyle factors.
We turn 36 next month. Perhaps this will finally be the year that we get tested and find out for sure!
Cori George says
Oooh, you have to get tested and tell me what you find out! :)
Annmarie Dallao says
My twin sister and I just got tested at ARCpoint Labs and after 56 years we found out we are identical!
Cori George says
That is SO COOL! :)
Mimi says
My sister and I have just had the results of a DNA test which says we are identical having spent 35 years believing we are fraternal. So many people said we had to be identical when we think we are so different, we got fed up with the old placenta conversation (our placenta looked fused and tests on it were inconclusive but they asured my mum we were not identical, she never questioned it as we have fraternal twins in her family) we decided the DNA test would be much easier and shut people up, I wasn’t prepared for the test to prove us wrong. Do you find it difficult to come to terms with? Like our identity is not what we thought?
Cori George says
I obviously can’t speak to Annmarie’s experience that you responded to, but I did feel a little weird when we found out our boys were identical, and we’d only been believing it for a year and a half! We decided to treat it as curiosity rather than just feeling like we’d been wrong. Twins are a crazy thing!
Kate says
I am a twin mom, and had them tested. The doctor said they would need a DNA test to know for sure. So that’s what we did. They are identical, which looking back now makes me feel silly that I even questioned it. But, when they were first born they did look very different, maybe because I tried to push one out for 3.5 hours before resorting to a C-section. Anyway, it is kind of my mission to inform others who tell me their doctor said theirs were fraternal, when they are clearly identical. 3 for 3 for me (they tested) 0 for 3 for those doctors. Same reason given as you were. Mine has separate sacs and placentas too, which made weird conversations when people would talk about my identical twins and I’d have to respond, “Well, we don’t know because they have different sacs and placentas” etc. LOL, I am glad it wasn’t just me having these conversations. Anyway, they say because of an early egg split, but mine are also mirror image, which means late egg split, so…… it goes to show doctors don’t know everything. Oh, and if by some chance you meet Mary-Kate and Ashley Olson, can you tell them this. A doctor told their mom years ago they were fraternal because of the separate sacs and placentas and it was never doubted, after all according to their mom, she can tell them apart and one is an inch taller. LOL, I know I am 4 for 4, I just need them to take the test. ? Thanks for the post and helping to inform!
Cori George says
Yes! Almost no one knows that it’s possible that fraternal twins are identical. I love telling people the story!
Alisa says
Your boys are just adorable! I was so excited to stumble upon your website after recently finding out my 19 year old daughters were identical and my sister’s boys! Crazy we both had twins and have a big family history of fraternal twins so leaned toward thinking they were fraternal. I love all the responses and reading similar stories. (I posted a response/reply under Robin).
Kris says
My sister and I were born 3 months and one week early. My mom was constantly told she wasnt having twins. That was before ultrasounds. When we were born, her doctors told her we were fraternal because we were in separate placentas. My whole life we heard the story that my mom didn’t believe we were fraternal. We looked identical. Now, after reading this article, I believe we may actually be identical after all. It makes me wonder if mom really knew best.