Twins in the womb.

Identical Vs Fraternal: What Your Doctor Didn’t Explain About Your Twin Ultrasound

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Categories Developmental Geekery, Fraternal, Identical, Multiple Types, Science of MultiplesTags , , ,

My Story

(or skip to the basics or the science)

Ultrasound of identical twins at 7 weeks. You can't see the membranes in this image.

I was 7 weeks pregnant when I had my first ultrasound. The doctor pointed out the shared outer sac (chorion) and the two distinct inner sacs (amnions). I didn’t need her to finish. Thanks to Advanced Placement Bio class in high school (embryonic development) I knew I had a miracle in my womb: identical twins. Once we’d called everyone we needed to share the good news with, I hit Google, and quickly concluded from their monochorionic/diamniotic (mono/di) state that my little ones had split from a single cluster of identical cells somewhere between 3 and 9 days after conception. I’ll tell you how I made the calculation in a little bit.

The Basics

Most people don’t know a whole lot about twins or higher order multiples, and are intrigued by them. Folks I run into are usually aware that there are two basic types, identical and fraternal, but often don’t know precisely what the difference is. Part of this comes from the term “identical.” In casual English, “identical” means “exactly the same,” and so people often assume that identical twins should look alike, act alike, and think alike. This assumption often gets extended to fraternal twins, in that they should look different, act differently, and think differently.

I don’t argue with people about whether my children look enough alike to be “really” identical, and instead give them a quick science lesson. You’d be surprised how many medical professionals, even obstetricians, don’t remember the science of twinning they covered in the depths of college or medical school, and therefore jump to possibly incorrect conclusions about whether a set of twins is identical or fraternal. Next time you need to explain the distinction to someone, feel free to use the visual aids below.

TWINS! Understand the basics with this clear primer. Click To Tweet

The Science

Identical multiples grow from the same fertilized egg and therefore have basically the same DNA. Fraternal multiples come from different fertilized eggs, and therefore basically share 50% of the same DNA, as do siblings conceived by the same parents at different times. Sharing a DNA template makes it likely that identical siblings will look very much alike, but DNA doesn’t predict everything.

My daughters, for instance, share their DNA, but have noses of different shapes and different hairlines, due to developmental differences that don’t appear to have a genetic basis. They’re also different heights, likely because one is a pickier eater than the other and because dysphagia related to macroglossia (trouble swallowing because her tongue was too big for her mouth) meant that she ate less than Sissy after she weaned.



Before I go much further into the science, let’s talk about the terminology we’ve been using.

Basic terminology to describe babies in the womb.

So, the embryo is inside the amnion, which is in turn inside the chorion. The umbilical cord traverses the two membranes to connect the embryo to the placenta, which collects nutrition from mommy for baby.

Twins in the Womb

Now let’s talk twins.

Monozygotic twins are identical ones. They started from a single zygote. (Mono means one.) Dizygotic twins are fraternal ones. They started from two zygotes. (Di means two.)

Monochorionic/monoamniotic (mono/mono) twins are monozygotic twins who share a single amnion and a single chorion.

Monochorionic/diamniotic (mono/di) twins, like my daughters, are monozygotic twins who have separate amnions and share a single chorion.

Dichorionic/diamniotic (di/di) twins are monozygotic or dizygotic twins who have separate amnions and separate chorions.

I try to make this clearer in the image below. With one egg and sperm, you can get one baby… or two babies who are mono/mono, mono/di or di/di. With two eggs and two sperm, you’ll always get di/di twins.

The different membrane configurations possible for twins in the womb. The chorion is on the outside, the amnion on the inside.

So here’s the trick. In the image above, you can’t tell the difference between the identical di/di twins and the fraternal di/di twins. And neither can the ultrasound tech. So, if you have di/di twins, chances are good that they’re fraternal, but you just don’t know for sure.

If you have di/di #twins, chances are good that they're fraternal, but you just don't know for sure. Click To Tweet

Reader Noura I was kind enough to share ultrasound images of her di/di identical twins, whose ultrasounds look just like those of fraternal twins. Remember, the mono-di stuff refers to the membranes around the babies, and not the numbers of eggs and sperm.

Dichorionic diamniotic identical twins at 6 weeks gestation.

di di twins 1st trimester

Reading the Ultrasound

What you can know about your twins zygosity from the ultrasound

So, in my little chart above, I had to note that there are extraordinarily rare cases of boy/girl identical twins, but this is a teeny tiny proportion of the population. If you ran across such a pair, you’d recognize them from the news. So, please, just assume that boy/girl twins are fraternal (dizygotic) or that one had a sex change. Either way, it’s not polite to ask. Girl/girl twins and boy/boy twins can be fraternal or identical.

Timing of Monozygotic Twin Split

Here’s a fun fact. The arrangement of amnion and chorion can tell those of us with identical twins when they split apart!

The membranes on your ultrasound tell you something about your identical twins schedule for splitting.

TTTS can be very serious and put both your babies at risk. The placental blood supply is shared unevenly, meaning that one has more than his or her share of nutrition and oxygen, the other less than his or hers. Many obstetricians will closely monitor mothers expecting twins to watch for TTTS. While it’s almost unheard of with fraternal twins, reader Halie H. wrote to us to say, “My di/di fraternal (boy/girl) twins’ placentas fused. They were born with one failed and one really really red placenta; they were sent off to be studied as an example of TTTS in fraternals.”

In #TTTS, the placental blood supply is shared unevenly between twins, putting both babies at risk. Click To Tweet

I’m not an expert on this stuff, but I do love genetics and studied it in college (although I ended up switching away from a biology major junior year). If you have additional questions, I’ll do my best to answer them.

Before I sign off, I need to give a big old shout out to I have been planning to write this post for years, but not having an artistic bone in my body, knew that I couldn’t do it justice without an illustrator. Thanks to the free online graphic design tool, Canva, I was able to create the graphics I’ve included in this post.

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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.

87 thoughts on “Identical Vs Fraternal: What Your Doctor Didn’t Explain About Your Twin Ultrasound”

  1. Such great info! I remember at my first ultrasound (at 19 weeks!!!) the tech knew I had twins, they were identical and they were both boys after about 30 seconds of looking. At the time I didn’t realize how much info they can get from the ‘sacs’ as we called them (my boys were mono/di).

    1. I had 3 embryos transferred and with my first scan at 5 weeks 4 sacs were seen. At my 12 weeks scan, the sonographer said 2 were identical, however, my obgyn said they cant be as they all have their own placentas and amniotic sacs, I am unsure what they are as one embryo that splits as far as I understand is known as an identical twin. I have read that identical twins can have their own placentas and amniotic sac. Can someone tell me if they are identical or not, please.They are all girls by the way.
      Katherine recently posted The Stealth TwinsMy Profile

  2. I’m always surprised at how many people pop up on various pregnancy message boards saying “there are two sacs/placentas so my doctor said that means they’re fraternal!” (At which I always point out that no, roughly 30% of identical twins also have two sacs and placentas – if they’re the same sex, you’ll have to wait until birth to find out for sure!)

    (Also you have a mistake in your last infographic – TTTS is a risk for any twin pregnancy that is (truly) sharing a placenta – so mono/di and mono/mono (but not di/di with two placentas that have grown together))

    1. I had no idea that mono/di twins could be at risk for TTTS!! In a way I’m glad I didn’t know, personally, since I would have been a wreck with my mono/di twins who didn’t have TTTS, but I would have wished my ob knew to look for it. :(

      1. My twins were also mono/di and also monitored for TTTS (which likely happened at the end of my pregnancy); I had weekly ultrasounds where they measured bloodflow through the girls’ shared placenta. It was very stressful, but according to my doctors, occurs in about 20% of mono/di pregnancies (this may not be accurate, but this is what I was told).

      2. There is a common mistake being made by Doctors, and by people passing along information about twins. TTTS is very broad and often the lead diagnosis in twins and yet, many twins actually suffer from T.A.P.S. TTTS is a nutrition TAPS effects the oxygen being carried via the blood.
        When looking for TTTS, during your ultrasound they base everything off of size and fluid difference. You cannot tell blood velocity via ultrasound.
        Naturally, I speak of this because I have Mono-Di twins that were diagnosed as TTTS but actually had Stage 4 TAPS. I had an emergency C-Section and we nearly lost both. They came out Red and White but nearly the same size in every way (so size discordance was not a factor.) My white baby was on the brink of death from lack of red platelets (oxygen) and required 3 blood transfusions.My Red was on the brink of a heart attack because of too much (his blood was thick, he had to be relieved of blood- he had enough for 3 babies, if you can imagine, that’s how much he stole and and that’s how thick it became.) Of course, I am not speaking scientifically, just basically.
        I mention this because the ONLY thing that detected my TAPS was during my N.S.T that I received on the regular. I stopped feeling them kick and was worried (at 35 weeks.) They did the test and one baby scored 8/8 while the other failed. They were testing for a rise or fall of heart rates and both remained the same. I drank sugar drinks and ice cubes to get them to move and nothing. I had an ultrasound and there fluid was perfect (what they look for in TTTS.) my tech had a ‘bad feeling.’ I had a ‘bad feeling’ and my OBGYN had a ‘bad feeling.’ But there was basically nothing to actually prove they were dying. This isn’t to scare people, this is make people aware. Twins are complicated, but ignorance makes it more complicated. The more aware we are, the more questions we can ask our doctors and hold them responsible to be up-to-date with current findings and the technology that is available to prevent this.

        1. My mono/di boys suffered from T.A.P.S. it was recognized in my weekly ultrasounds at 27 weeks. I had to deliver them via c section at 30 weeks. Anemic baby’s heart rate was dropping so low. I was monitored for 2 weeks, 24hrs a day, before his heart rate started to drop and the doctors knew it was time. There is a lazer surgery that can be performed to fix T.A.P.S. if it is caught before 27 weeks. Of course, I had missed the deadline by 3 days. Very scary thing. Luckily we had amazing doctors that knew what they were doing every step of the way. Our boys are now 14 months old and you would never know they had T.A.P.S.!

      3. I’m glad your twins did not have TTTS. Obs should be enlightened on these issues and watch out for their patients who may be experiencing this so as to give proper medical assistance before it’s too late.

    2. Thanks for the correction, Erica! I’ve updated the graphic. Please don’t hesitate to point out other mistakes I may have made!

  3. Another fun fact – if the first ultrasound is early enough, you can tell if they are some form of mono (either mono/mono or mono/di) or di/di – if you see a big black blob with two babies, they’re identical for sure – depending on the resolution of the ultrasound machine you may or may not be able to see the separating membrane that would indicate mono/di. If you see two black blobs with a baby in each, they’re di/di (and may be identical OR fraternal).

    1. Yep! Our ultrasound was at 7 weeks, so we could see they were mono/di. I’m hunting through my papers to see if I can find a copy of the ultrasound with the clear membranes to post!!

    2. Very interesting! I had my first ultrasound at 5 weeks and it was the black blob with 2 eggs. Immediately they scheduled me to be monitored by another OB where they had the advanced ultrasound machines. Once I was checked there (weeks later) they could see a very thin line of the membrane and they shared a placenta. Can anyone give more information about genetic testing on twins? I’ve read that the only way to tell if you twins are identical is to have testing done.

  4. My boys had two sacs so my Dr. Automatically said they are fraternal. My first ultrasound was at 3 weeks. Is there something I should look for that might show they might be identical?

      1. Well if they have different blood types then you’d know they were fraternal. Otherwise you’d have to get a DNA test.

    1. Another “spot check” can be blood types – I know they tested my girls at birth (I can’t remember if they did my youngest, the big girls were (later term) preemies, and were sent to the NICU so the typing may have been part of that rigamarole) – if they have different blood types, they’re fraternal :)

      (And, just by informal review of parents posting on the twinstuff forums, my gut feeling is “if nobody but you (and close family) can tell your twins apart, they’re identical”)

      1. I did call the hospital after they were born and asked about blood type but no one could help me… They even had surgery there before they came home, so I would think it would be in their medical records.

        1. It would be in their records. You may have to go to the medical records department of the hospital and equestrian the records on writing…but you are entitled to a copy of them…all you have to do is ask!

        2. Your’s sound very much like mono/di, in which case identical. No testing needed if they shared a placenta early on and showed only one dark sac with two babies early on. Testing is needed for Di/di identicals.

  5. It was when we discovered that we were pregnant with mono/di twins that my husband started to suspect that he and his brother were in fact identical and not fraternal, as they had been raised to believe. Their mother had understood and thus told them that because there were two amniotic sacs, they were fraternal. Mind you, she discovered she was pregnant with twins at 7 months, after an X-ray where they saw three spines instead of two. There were no routine ultrasounds in France in the ’70s.

  6. On another topic, “identical” and “fraternal” in English is still much better than the terms in French: “true” or “fake” (vrais ou faux).

    1. Eeewww. I didn’t know that. That’s pretty awful. :( I realized that I didn’t know the Bengali words for identical and fraternal, so I looked them up. “Fraternal” wrt twins wasn’t even in the dictionary, and “identical” was a 4-word phrase meaning, essentially, “same genetics” which I doubt is common parlance.

  7. Thank you for explaining to me how and why it’s hard to tell if di/di twins are fraternal or identical (unless you know, like me, how many eggs we put in and how many children we got back). I honestly never understood it until now.
    You should have been a teacher!
    (Although I still don’t get that math thing you were teaching your girls a few weeks back, using the quintuplets or sextuplets or whatever they are, as a reference. My head is still spinning from that one.)

    1. Although even IVF isn’t a surefire way to guarantee fraternal twins. Quadmama had 3 eggs and ended up with two of her quadruplets being identical!

      I really do love teaching. I dropped out of grad school on realizing how little teaching I’d actually get to do. :(

  8. I am going to direct everyone I know to this post! Very informative! Our first ultrasound was at 6 wks, and there were two sacs, though at the time we could only see one embryo. At 8 weeks, we could see both babies and sacs, so my ob/gyn assumed they were di/di. Then after another person examined the ultrasound, they decided they were mono/di and we were referred to a high risk specialist (to monitor for TTTS as well as specializing in multiples pregnancies). It actually went back and forth as to whether or not they were mono/di or di/di until the experts settled on mono/di. There was only one placenta and there didn’t seem to be an indication that it was fused, so we’re rolling with mono/di. Might have a DNA test at some point to find out for sure, but even the so-called experts have a hard time telling at times!

  9. Hi I just want to say that this is very informative as a mother of twin girls (who look VERY much alike). Everyone asks me (or rather TELLS me) if they’re identical. I have just asked my midwife (who was supposed to test the umbilical cords at birth but forgot) and her and the drs have said mine aren’t identical but only blood tests will determine that for sure. My bubs had 2 sacs and 2 placentas but I had read that they can separate early on and this article has just confirmed that for me. Now I really wamt to get my girls tested because even I have trouble at a quick glance of telling who’s who lol

  10. Sadia, thank you so much for pointing out the possibility of identical b/g twins. It’s a pet peeve of mine that so many people assume this isn’t possible. My understanding is that it would first require a XXY chromosomal abnormality in the fertilized egg, which would then split into a XX zygote and an XY zygote – genetically identical save for the Y. But, as you noted, this is very rare.

  11. Hi great page. I had my 1st pregnancy scan at 6 weeks – di di was told fraternal non-identical. Confirmed at 8 wks, 12wks and when born by c-section. Both girls and had difficulty telling them apart from the very start. Several medical issues the same. It wasn’t until their last neo app that the Dr who always asks me if they identical explained that it is possible that di di s could be identical but the only way they would say for sure is by blood test. I went to the British Multiple Births Association website. They have section on zygosity testing through Kings College London. You get a kit to take mouth swabs from both. A week before their first birthday I have found out that their DNA matches, they are monozygotic identical!

  12. we found out we having twins at 6weeks but in the scan report only they mention only diamnotic twins but they have separate sacs, but i don,t konw what kind of twins for me please tell me

  13. Thanks! I am fascinated with our mono-di twin boys and the science of it all! Have you researched where/what causes ‘Mirror’ twins? I would love to hear about that aspect of twins!

  14. All the way through my pregnancy I was told my twins were identical as they shared a placenta. This was from scans. Then we had TTTS and the two girls were born at 31 weeks. The placenta they “shared” was clearly healthy on one side and not so on the other, different coloured. I always assumed they were identical until about a year old. They are different heights, different skin tone, one slightly tanned, one has thicker waiver hair one thinner straighter hair but they do look like they are sisters. I was told later the placentas could have fused together. I just wonder if they are identical! Haven’t had dna test and they do look different so I would feel silly getting one! Has anyone had any experience of the placenta fusing??

    1. There are quite a few documented cases of fused placentas. While it’s very rare, there are also cases of fraternal twin fused placenta TTTS.

  15. I myself am also an identical twin so I thought it quote neat I has momo/ mono twins. Ppl always say my sister and I are mirror twins not sure if that is true but I’m left handed and she is right. We have so many opposites. :)

    1. Me and my identical twin sister are like day and night! We look alike and think alike(sometimes), but we have so many different personality traits and some different physical traits! I also think that it’s pretty cool that you have identical twins as an identical twin, I’ve only met a few sets of identical twins in my life so far.

      1. I realize this is an older post but I came across it while looking for twin info. I have an ultrasound today to find out if there are two. I was curious if you could tell from the ultrasound if they will be idental and fraternal.

        Anyway, everything I’ve read says identical twins aren’t hereditary but my Dad’s side of the family has 6 sets of twins across 4 generations and they are all identical. 3 of those were my first cousins so I grew up around identical twins and they were difficult to tell apart and all of them would try to trick the other family members. I find it so hard to believe that there is no genetic link. We do have a large family but statistically we should have some fraternal twins in there and we don’t. How does science explain this? The only twins I didn’t see with my own eyes were my great uncles. Leo and Lee. Lee didn’t in his first year. I suppose it is possible they could have been fraternal but looked alike so it was assumed? The other 5 sets, I grew up around and they are definitely identical.

  16. We have Di/Di Identical twins… The Ultrasound tech and even our initial OB/GYN ( had to change at 29 weeks) swore up and down that because there were 2 sacs and 2 placentas they HAD TO BE fraternal… Definately not the case! We had boys, and just to be sure we had genetic testing done to prove that they were identical.

  17. Just FYI, it is extremely (EXTREMELY) rare, but you can have a single chorionic sac with fraternal twins. There was a sudden (minor) freak out fairly late in my pregnancy (30-ish weeks? I don’t remember right now!) because we had always assumed they were fraternal, but with a more detailed scan/new type of machine, it was abundantly clear that they shared a chorionic sac. But at birth, even as squishy newborns, it was immediately clear that they were 100% not identical (one blond/blue, carbon copy of husband and one brown/green, carbon copy of me). So, yeah. Research still isn’t clear on how/why it can occur, but it does, indeed, occur. (My twins may both be boys, but considering that they don’t even look like brothers, that’s about the only identical thing about them!)

    1. That has to be what we have. We were told fraternal by looking at the ultra sound but had a pathology report done after birth which came back as one outer chroion and one placenta. 2 sacs identical but my boys don’t look identical. One has a shade darker hair which is curlier. He also is about 2 inches and 8lbs bigger at 2 1/2. They do favor but no one has trouble telling them apart. I am so glad I read this. It has been driving me batty.

    2. I am old and sonograms were fairly new when I had my children. They did not even have them with my first. My third were twins, boy/ girl. She had blond hair with blue eyes and he brown hair and eyes. With my second set I had a sonogram very early, which surprised me. I think I was only 5 or six weeks and didn’t even realize it was possible. What I saw on the screen was just one blob but it was larger on one side that the other. I already knew I was pregnant and with twins :) I am going to have to dig out any old pictures of the scans I have after reading your article. They look nothing like what you have today which are amazing! I have gotten to see my grandchildren in 3D!
      The second set were boys and they shared a bag and placenta. At the time of birth the doctor was surprised by this, the different size early on suggested they were conceived about 2 weeks apart. I thought they were identical but other than same hair and eye color they really looked nothing alike. He said at the time that maybe everything at fused together. I have tried to find pictures of what they looked like on the first one and haven’t seen any that look even close to it.
      They have been studied their whole life by Washington University in Mo and I am thinking of asking if they might be able to look at the DNA test they have on them and tell me what they really are. I have read many articles with many theories over the years and things seem to be changing rapidly now so maybe I can finally get an answer :) I don’t know why it seems so important to me but it is.
      Thank you for such a great site. It is one of the best I have seen in all my years.

  18. According to my doctor and every one else in the world I’m having fraternal (di/di) twins because they have two different sacs as well as two different placentas. I’m currently 24 weeks pregnant with boys. I’m glad I read this, there is a lot of info I have not yet received from my doctor. Thanks

  19. This is the best post I have seen on twins, in Australia we call mono/mono twins, momo’s. My momo girls are 3 now and it was always really difficult to explain the higher levels of twins to people and they are always so curious! I’ve saved this for future reference and as a tool to help explain to the girls how special they are later on. Thank you!

  20. This may sound ignorant in asking, but here goes: so some reptiles that lay eggs in the dirt the gender is determined by the temperature of the nest. What then determines the timing of when the egg splits for each kind of twin? Is it predetermined within the sperm/egg? Maternal pH? Any idea?

  21. Can someone and/ or Sadia answer this question for me? I have 21 month old identical boys. They were identified as di/di at all of the scans. I was told I was having fraternal twins. When the boys were born, we were told by the nurses that they had the same blood group. They also looked identical so we questioned their fraternal-ness and had them genetically tested. They are indeed identical. In addition to that, they are mirror image identical. One is left handed, the other right. Their head crowns are on opposite sides and the hair swirls in opposite directions. How can di/di identical twins also be mirror image? I have been told that di/di twins’ egg separates between 0-3 days like your graphic suggests. I have also seen graphics that explain that mirror image twins’ egg separates between day 9-12. These are two opposing bits of info. What is the truth?

    1. I was researching mirror image twins a few days ago and came across a theory that the instance of mirror image twinning has nothing to do with WHEN the eggs split but rather HOW they split (horizontally vs. vertically).

    2. I don’t have any more info for you, but I also have di/di identical mirror image twins. I have wondered the same thing!

  22. This is a super detailed post on how to know if your twins are identical or not. Mine is Mono Di. When I learned that I will be having twins I read a lot and was also surprised that there different kinds of twins! Even my OB didn\’t know if they are identical or not.

  23. Just wanting to throw in my own experience:
    We found out we were having twins at our first appointment (10 weeks). After our first official ultrasound (12 weeks) we were told they were di/di. At our 20 week u/s we were told they were boys. Throughout the pregnancy we also had multiple techs and doctors tell us they were fraternal either because they had two sacs or because the placenta placement indicated they were dizygotic. Well, it’s been nearly a year and they look SO much alike that we finally got them tested; they are monozygotic! How can so many doctors and techs in this field be so uninformed?!

  24. What a fun and interesting post to read! I have a set of mono/di girls who are now nine years old. My OB would never conclusively say whether they were identical or fraternal, he always told me that if we wanted to know for sure we would have to have genetic testing done on them. My girls were in separate sacs, yet shared one placenta. I developed TTTS at 30 weeks and had to be monitored very closely over the next seven weeks before I delivered via c-section. Baby A who had the high blood cord pressure has always weighed just a little more, been a little bit taller, her hair has always been thicker than Baby B who had the decreased pressure. I think it would be an interesting study to conduct as I have my own theory that it is the decreased blood supply that makes these twins the smaller of the two. When they were first born, I woke in the hospital to find two nurses with their heads bent over them debating on whether they were identical or fraternal. To be honest, they really looked nothing alike at birth. We spent the money on the genetic testing, but if I had only waited three months I would have been able to see that they were identical.

    1. Thanks for your comment, Amy. That’s a post I’m working on. I’ll be sure to email you with a link once it’s published!

  25. Sooo….after reading all of this (which greatly went over my feeble little head), should I conclude that my twins may, or may not be identical? My 19 year old twins tell everyone they are identical, even though I’ve always told them my doctor wasn’t sure. They were in separate sacs, but shared one placenta. My doctor said that if there were two placenta’s fused together, it was the best fusion he’d ever seen, so his guess was one placenta. One weighed 5/11 and the other was 6/1. They were delivered by C-section at 35 weeks. Is DNA testing the only way my girls will know for sure which type of twins they are? I ask, because DNA testing is pretty costly. I should probably add that my girls were very difficult to tell apart until they reached their teen years. Would greatly appreciate knowing. Thank you, Barbara

  26. My 13 year old identical twins are mono/mono we lost the ultra sound pictures while moving house, they are also mirror twins one right one left, we have five children and have just found out I’m 7 weeks with twins again, 2 sacks,with our identical twins our doctor and ob knew they where identical and we’re born 3 months early due to twin to twin transfusion, scary but they are great now, we where lucky enough then to have brilliant info given to us about the different types of twins I still have it

  27. I’m a mono mono mirror. Identical twin. My sister and I have so much fun with people. Our parents can’t even tell us a part on the phone, and we are 54 years old. We switch the phone back and forth between us to all our friends and family. My sister was born first then I was breech birth 7min. Later. Life being a twin is the best thing about our lives. We live together. We used our own twin language until we started kindergarten school and didn’t need to make any friends cuz we had each other, so they held us back to re-do kindergarten. This time we went at different times. Our boyfriends get so jealous when we want to spend time together and we don’t know what to do about that. Does anyone else have any advice? Sheri & Vel Amsberry

  28. Great website! Love the info and graphics! I am the grandma to be of mo/di girls that are 21 weeks gestation. We just found out they have TTTS. I know it’s treatable but very scary! Anyone with advice for me and my son and daughter-in-law? They are going for an evaluation next week for possible treatment. Thanks!

  29. I’m having twins, i’m currently 7 weeks . but I’m so scared something may happen die to vanishing twin or misscarriage . how do i now worry so much?

  30. I just found out im pregnant with mo mo twins, 7 weeks, I’m very nervous because I lost my firstborn son at 38wks, I think that the egg split so my angel could come back to me in a way, but is there a way to be less stressed or more information about safe healthy momo twins? Ive heard they’re the most at risk twins. And im already high risk.

  31. Hi! I’m having 13-14 weeks mono/di twins. Their weight difference is 10 grams. My obgyn said that they are identical, & thanks to you, Sadia, now i know all about it.
    But are chorion & placenta different? If so, what is the difference? I’m still confused. Hope you or anyone else could explain it to me. TIA!

    1. Aria, the placenta is an organ that connects the baby/babies to the mother’s womb wall. The chorion is the outer bag that contains the baby/babies. Think of the placenta as a cushion filled with nutrition and the chorion as a balloon with another balloon (the amnion) inside.

      1. Hi Sadia!

        My obgyn said that i had 1 placenta and 2 amnion sac, so my twins are identical & called mono/di twins.
        If they share the same placenta, is that always mean that they share the same chorion?
        Or maybe i heard it wrong about his statement for mono/di twins?

        1. A shared placenta COULD mean identical twins, or it could be a fused placenta from fraternal twins. Without a shared chorion confirmed, it’s hard to know.

  32. Okay guys I’ve read and read and I’m still so confused! This is my first set of twins, but they will be my 4th and 5th babies

  33. Hi
    I’m currently 16weeks pregnant with Twins.
    We only found out that we were carrying twins at our 12 week NT scan.
    The sonographer said they are mono/di twins (same placenta-seperate sacks but same chorion) and the membrane that separates the babies is quite thin.
    The sonographer zoomed in and couldn’t see a spot in the placenta where it had fused so thinks that the babies are identical BUT twins run in my family (sister has fraternal boy/girl twins also)
    I’m assuming that it’s safe to say that my bubs will be fraternal too??
    Too much of a coincidence not to be??

  34. We just found out we are having twins. Due in August, so we still don’t know for sure if they are fraternal or identical – although they were each in their own sac. Hard to tell in the sono if there is one placenta or two. Fraternal twins run in my family, so maybe so!

    How were your appts? I was told we are technically “High risk” this go round, but what does that mean U/S and appt wise? obviously there would be more towards the end or if there were any new risk factors, esp something like TTTS.

    1. May I recommend MoDi groups on Facebook? You should see an MFM rather than a regular obstetrician. The latter won’t know what they don’t know!

  35. Hi. Thank you for posting all this information. It’s very helpful. Thank you.
    I’m about 10 weeks along and my twins are Di/Di. How can I find out if they are fraternal or identical? Based on your chart, they could be both. Do you know how I can find out?

  36. I am a twin born in 82. Little was known about the 4 types of twins back then. What I know for sure art this moment is that mom was told fraternal but we have the same blood type. She was always a little taller and weighed more but we looked just a like as babies. This article has helped me to ask my mother more questions about our birth. I wanna know if there were 2 placenta or one

  37. First of all, sorry for my English… It’s not my natural language, and this subject is too technical for me…

    I would like to tell that monochorionic/biamniotic can be fraternal and identical twins.

    My wife and I are waiting for our babies… We are just in the 14 week, and we had the first ultrasound two weeks ago.

    We had the biggest surprise we ever could imagine, and when the ultrasound was coming to the end, the doctor moved the machine, and told us: wait, wait, wait… Here is another one!

    We were shocked, so we couldn’t ask everything we would like to ask. The only thing we had clear (because the doctor told us) was that it was monochorionic/biamniotic, and that they were fraternal twins.

    When we arrived at home, we started to look for information about that kind is pregnancy, because in my head, something doesn’t mach…

    Why the doctor told us they were fraternal, if there were only one placenta?

    We had a lot of doubts, so we came back to the hospital the last week, to confirm the conclusion I get after my investigation.

    Sometimes, in fraternal twins cases, the placentas can be unified… Or can be as much closer than the ultrasound can’t difference if there is one or 2 placentas.

    So we asked the doctor: how can we know if they are going to be identical or fraternal?

    And the reply was really simply… And obvious: you will know when you see them for the very first time.

    We don’t still know the sex of the babies, so maybe, if they are boy and girl, we can get the answer before the birth… But if they are two boys or two girls, we have to wait until the birth!

    So the only situation you can confirm they are identical is if there is mono/mono… The other 2 situations can be fraternal or identical twins.

  38. Hi Sadia,
    Thank you for sharing your graphics! They have been so helpful for my husband and I. We show them to people all the time when explaining twins and that ours were mono di.
    Thanks again!

  39. My twins are di/di fraternal. The doctor even told me there was a three day gustational period between the two fetuses. So I basically got pregnant with baby A and three days later became pregnant with baby B.

  40. Hello. I am 8 weeks and 6 says. At my first ultrasound (7 weeks 5 days) we saw two sacs… one heartbeat was picked up almost immediately while the other one had to be detected vaginally! Now I am getting heartbeats from both babies but when we see them one sac always looks empty. He has to take separate pics of babies. Is it weird that the sacs are right next to each other and one baby cannot at all be seen? They are now measuring 2 days apart! I hope this isn’t horribly confusing!

  41. I did a scan @ 5 weeks we saw 2gestional sacs,then later 1 went out of sight.i be scheduled for another scan in a month time.could there be twins in there?

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