Identical Doesn’t Mean Identical

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If I didn’t know from an early ultrasound that my daughters were identical twins, I would have just assumed that they were fraternal. I’ve known fraternal twins and different aged siblings who’ve looked more alike than J and M do, at least to my eye. We still get asked if they’re identical occasionally, but most people are surprised to learn that they are.

J and M, posingAs M likes to point out, her widow’s peak hairline makes her face heart-shaped, where J’s is oval, thanks to her ruler-straight hairline. J is built like a soccer player, all lean muscle and power, while M has a typical dancer’s frame, birdlike and flexible.

J inherited Daddy’s single dimple, but M didn’t. J’s cowlick is profoundly untameable, while I can get M’s hair to hang down nicely with a little effort. On the other hand, I can part J’s hair in the middle, put it in pigtails, and have her hair stay generally well-behaved all day. M’s part, on the other hand, clings stubbornly to its location. It’s stronger than any combination of hair elastics, gel, bobby pins and effort I’ve been able to come up with. I’ve stopped fighting it, even if it does cause her pigtails to noticeably differ in thickness.

M was born with a facial cleft, which hasn’t needed any surgery so far. I hope it stays that way. Rather than the more familiar cleft palate, her frontonasal dysplasia is higher up in her face, and is the cause of her defined widow’s peak. It also causes her eyes to be more widely set than her sister’s and impacts the symmetry of her nose. She hasn’t had any complications from her condition, so we don’t spend a whole lot of time thinking about it. On the rare occasion that a child asks why M’s nose is funny or little, I say that it’s so we can tell her apart from her sister. That answer has always satisfied diminutive inquisitors.

Every now and then, though, I catch a glimpse of Sister in the face of one of my daughters, and the sameness makes my breath catch.

Adult identical sisters hold 4-year-old identical sisters.I’ve come to enjoy the opportunities I get to share the science of twinning with strangers. I’ve learned to explain in a few words that identical twins are identical(ish) at the level of DNA, but are otherwise completely distinct people. Still, I’m taken aback every time I participate in the following exchange:

Stranger or acquaintance: Are they identical?
Me: Yes.
Stranger or acquaintance: No, they’re not!


Do you know whether your multiples are identical or fraternal? Does it make any difference?

Sadia is a business analyst living in El Paso, TX. Her twin daughters, J and M, will be turning 6 next month.

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Sadia (rhymes with Nadia) has been coordinating How Do You Do It? since late 2012. She is the divorced mother of 10-year-old monozygotic twins, M and J. They live in the Austin, TX suburbs, where Sadia works full time in information technology. She contributes to a number of parenting websites and magazines and also runs The Mommy Blogging Guide, where she answers mommy bloggers' technical questions.

13 thoughts on “Identical Doesn’t Mean Identical”

  1. Yes I can relate! My girls are also identical and we found this out at our first ultrasound when they were 12 weeks old…they shared the same placenta thankfully they had a thin membrane separating them. Baby A was always a little behind in weight so once they were born it was easy to point out who was who! Baby A (who we called Anna) is still 2 pounds smaller then her sister Sara. Anna has a much narrower shaped head then Sara who has a rounder shape face. Sara is also a couple inches taller. Most people who don’t know them think they are identical, but I can hardly believe they think that as I see all their differences :) Family and close friends who spend time with my girls have no trouble knowing who is who. They are almost two and I am looking forward to seeing how they continue to grow…if they keep their own look or if in time they will start to look more and more alike. I remember reading before they were born that some identical twins could look less alike then some fraternal…I thought that was odd, but now I know this is true :)
    I always get the question if twins run in the family…my dr told me that genetics has nothing to do with identical twins, that there is no scientific proof as to why identical twins happen…it just happens and is a miracle! but that fraternal twins are genetic…it is hard to explain that to people, and sometimes I don’t bother 😉 There are so many comments and questions I get…and it is funny to me that everyone seems to ask or say the same things! lol!!
    Thanks for your post, I enjoyed reading it. Your girls are beautiful!

  2. I have identical twins and we didn’t find out that they were identical until they were 2. Throughout my whole pregnancy, they said that the twins were fraternal. They were in seperate sacs and so they just automatically thought that they were fraternal. When they were born, they were 9oz apart in their size. There was a visual size difference. Once they hit around 6 months, they have been very similar in their sizes, not differing more than those same 9 oz in weight like when they were born, not more than a 1/2 in in height, and not more than a 1/2 in in head circ too.
    I thought that they looked identical since they were born, but that was just me. The funny thing is that once we found out they were Identical, they didn’t look so identical to me anymore. I guess I am just a silly mom! Thank you for the story!

  3. My boys, now 2.5, were di-di in the womb. The drs and we assumed they were fraternal. They were 6 oz different in size at birth, but they quickly evened out. We started to notice that they looked more similar than just brothers might look, so as a 1st birthday present we did the DNA test. Lo and behold, they were identical after all!

    We did the test because we thought it would be nice for them to know definitively, and because it could be important medically at some point. But mostly just because it was fun and cool to know! I am always in amazement that they exist, my little genetic miracles, hahaha. :)

  4. we had a DNA test done when the boys were a couple of months old that showed they were, in fact, all identical. (if i knew then what i knew now, and if my OB hadn’t been an idiot, we would have known from the beginning.) they’re 4, and i still sometimes have trouble telling them apart at a glance, but sometimes i look at them and think it’s amazing that strangers can tell they’re identical.

  5. My boys are fraternal but I have people argue that they must be identical all the time. Even though one is now 3-4 inches taller and a good 5 lbs heavier at age 2.5. They saved us the trouble of any testing by having different blood types.
    I think people just sort of check their brains at the door when they see twins or triplets. I actually had a woman ask if they were a boy and a girl when they were a week old, I said no, two boys, and she asked “Are you sure, that one has a green blanket?” Seriously. Can’t make this stuff up.

  6. My boys are fraternal, they have different hair color and one has always been an inch taller and a pound heavier. I get zero twin questions even when I dress them alike. People always assume one is an older sibling! However, I was told by my doctor, while pregnant that they were identical. I was told this at the hospital after the “lab” analyzed my placenta (or whatever). Just goes go show, you cannot believe everything the “professionals” tell you!

  7. Mine are ID and I’ve known since the first ultrasound at around 8 or 10 weeks. I knew then because there was one placenta and they couldn’t see any membrane at all, and they told me I had a mo/mo pregnancy. Eventually they were able to see a whisper of a membrane (whew!).

    Further solidifying it was that we had significant fluid imbalances determined to be a precursor to TTTS. So there was no doubt the whole time.

    Even though they were a pound and a half different in weight at birth (and at 3.5 and 4 pounds it made them really different in size), I had a super hard time telling them apart unless they were right next to each other. They are a year old now and I am finally able to know who’s who at a glance — most of the time.

    So anyway, I get crazy people all the time either assuring me that they are identical (ummm pretty sure I don’t need a non-medical stranger to tell me that) or that they definitely are not identical because they look nothing alike. That one always gets me.

    I also feel compelled to give the fraternal-can-be-genetic-identical-is-not speech to everyone who asks me whether twins run in my family. I don’t want to give a genetics lesson but I can’t help myself!

    As to whether it makes a difference… I guess maybe it doesn’t really. But it does to me. I’m not sure why. Maybe it’s because I have two adult sons and had no intention of having more children. I didn’t even think I could. I was terrified when I found out I was pregnant and wondered how my “only” child would fare. Then it seems like the universe said, “ok, let me just split this egg in two, and you won’t have to worry about it!” LOL

  8. I guess I’ve never really considered the other side of this- my twins are very fraternal- we have been able to tell them apart since the moment they were born. But strangers are always trying to convince us that they’re identical. Off the top of my head- they have different blood types, different eye colors, one has straight hair, one has curly hair and they have completely different builds. But yep, they must be identical. Lately, since they’ve turned 1.5, I have been getting more questions about how close in age they are. My firstborn weighs 4 pounds more and is off the chart for height and weight so I think people assume she’s a small 2 year old and my secondborn is a large one year old. I like to mess with them and just say “6 minutes.” It always takes them a few minutes to process that and realize they’re twins.

  9. My six-month-olds are boy/girl twins, so of course they’re fraternal. As we were told to expect, we do have people ask if they’re identical every few weeks or so. I’ve even had someone ask, “Are you sure? They look exactly the same!”

    (No, they really don’t.)

  10. We get asked that all the time. Our 16 month old boys are identical, but when you spend 20 minutes with them, you can see minor differences that to me, the mom, are hugely apparent. I like that they are a little bit different. I feel that it will give them some sort of individuality (at least with their appearance) and then maybe people won’t call them “twin” because they don’t know who they are talking to. And at the same time, I kinda like that they are very similar in their appearance. I feel that it makes them more unique. That’s one of the issues I’m finding with being a parent of twins…you always have conflicting emotions! (that could just be a parent thing too =)

  11. We were told that our babies were fraternal because there were two sacs and two placentas that had fused together (though one ultrasound tech that it was just one). Our girls look almost exactly alike, have the same hairlines, hair and eye color, body shape (though one has always been slightly larger), blood type, etc., and most people cannot tell them apart. Family can almost always tell them apart, and they do look different to me. We’ve had pediatricians and a geneticist tell us they are identical, but we haven’t bothered to have them tested. It’s funny, because when we thought they were fraternal and said so, people would argue that they had to be identical. Now that we suspect they are identical, people argue and say the are fraternal!

  12. my girls are definitly identical thay like beths girls have the same hairline and color ther eyes are the exact same color and thay are the same blood type and both like M have “dancer”builds
    and have dimples in all the same places thay are small for nerley 11 and onley wagh about 80 pounds the only difference i’v notied is that annie has a tiny tiny relly faint beautey mark under her left nostrill but this can only be noticed wehn looking reeeeeeeeeelllllllllllyyyyyyyyyyyyy closeley and my hubby and friends dont’notice anything let alone the girls.and ether way the only difference it would make is that thay would be thay would not dress alike

  13. We don’t know what our twins are. Fraternal twins are all over my family so everyone just assumed that my girls would be fraternal especially considering the two sacs and two placentas. My girls, however, look so much alike that I often confuse them. Same build, same hair and eye color, and even moles in the same place! They have done everything within a day of each other and the timing of their milestones have been very different from their older sister. People always assume that they are identical and I tell them that I just don’t know.

    My hunch is that my girls are Polar Body Twins. It just seems to fit who they are and while I’m curious to know for sure, I’m not sure if genetic testing could tell us that definitively. Someday if the girls really want to know, they can choose to do the testing themselves.

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