Mono Di Twins: What You Need to Know

Almost one third of twins start as just one egg, which then divides and leads to a pair of wonderful identical twins! But depending on how late the egg splits, can lead to very different situations for you and your babies.

In most cases the egg splits early, which leads to a standard and generally uncomplicated pregnancy, but if the egg decides to split later, it can lead to situations like mono di twins.

mono di twins

Monochorionic Diamniotic twins have their own amniotic sacs, but share a placenta.

Because they come from the same egg, they are always identical. Sharing a placenta can lead to complications in your pregnancy, but recent advances in medicine have limited the risks of mono di pregnancies, so now it’s only considered a medium risk, rather than the high risk it would have been even ten or fifteen years ago.

What Does This Mean for You and Your Twins?

Generally, learning that your twins are mono di is nothing to worry about. The mono di twin survival rate is around 97%, with only around 15% of mono di cases developing into a situation that requires close monitoring or hospital intervention.

This means it’s incredibly likely that your mono di pregnancy will progress exactly like any other twin pregnancy, with no complications or problems arising.

And even if problems should arise, scientific advances give your twins the best chance of survival, with a relatively simple and safe medical procedure that’s available now that can deal with the major problem that faces this sort of pregnancy.

What Are the Mono Di Twins Complications?

Because they share a placenta, complications and problems occur with more frequency; the main ones being Twin to Twin Transfusion Syndrome, (or TTTS) and Twin Reversed Arterial Perfusion sequence, (TRAP.)


Twin to twin transfusion syndrome is caused when there’s an imbalance in the blood flow from the placenta to each of your twins. Put simply, one of your twins is getting more blood than the other one, and this means they are also getting more oxygen and nutrients.

This can lead to complications with both twins. The twin receiving the lions share of the blood will produce more urine, which leads to a larger bladder and potentially even heart failure.

Because they’re receiving more blood and producing more urine, this can cause an excess of amniotic fluid, which causes the womb to expand and can lead to premature labor and delivery, which could lead to the loss of one or both babies.

The twin receiving less blood will develop anemia through lack of red blood cells, as well as producing less amniotic fluid, which in severe cases can cause the amniotic sac to stick to the fetus, and the fetus to potentially stick to the inside of the womb.

Even if the twin receiving less blood dies, the surviving twin is still at risk, because the shared blood vessels can cause major complications in blood flow, oxygen and nutrient levels. Over time, this can lead to growth deficiencies and other problems.

TTTS is generally treated with one of two methods, with a third option being taken only in the worst circumstances.

The first is amnioreduction, in which excess amniotic fluid is drawn from the larger twin’s amniotic sac, which reduces the chances of premature birth, decreases the strain on the mother and normally equalises blood flow between your babies.

If surgery is needed, a procedure called laser ablation is used, in which doctors seal off some of the blood vessels in your placenta to even up the amount of blood going to both twins.

In the rarest and most severe cases, it’s possible for doctors to close off the blood supply to the twin receiving less blood completely, so that the twin receiving the most blood can survive. This option is only ever taken when there is no other choice.

Thankfully, all of these options have incredibly high success rates, and caught early enough, TTTS is a situation that can be managed and dealt with, no matter what complications might occur.

TRAP Sequence

In 1% of cases, mono di twins can develop into a situation called twin reversed arterial perfusion sequence, or TRAP.

What this means is that one twin develops without a heart, and normally many other internal organs, and is connected to the healthy twin with a large blood vessel.

Because they have no heart structure, the twin with no heart (called the acardiac twin) receives all their blood from the first twin, or pump twin. This causes the pump twin’s heart to have to work harder, because it is supplying blood to two bodies.

Treated properly, the survival rate for the pump twin is very high, with around 85% going on to live normal, healthy lives. Sadly, the acardiac twin cannot survive with no heart, and will not survive after birth.

Depending on how your twins TRAP sequence progresses, it may require surgical intervention, in the form of radiofrequency ablation. This procedure seals off the blood vessels in the acardiac twin, stopping the pump twin’s heart from having to work so hard.

Thankfully, even a procedure as delicate as this has a fantastic success rate, with a survival rate as high as 9 out of 10 for even the worst case scenario.

Will Having Mono Di Twins Affect Your Pregnancy?

Because you’re having twins, you’re already at a higher chance of premature birth, lower birth weights for your babies, and it’s also likely that your doctor will recommend a caesarian birth.

Other than this, once you know you’re expecting them, it’s normal to face a barrage of scans and tests. This is just to make sure that both of your babies are developing normally, with none of the complications we’ve just talked about.

Happily, as long as your babies are both healthy and don’t develop any of the syndromes we’ve discussed, you can expect a completely normal pregnancy.

Are you expecting mono di twins? Any interesting stories or encouragement for new mothers? Let us know all about it in our comments section.

  • April says:

    I just had my anatomy ultrasound at 19 wks and just found out we were having twins and monodi twins at that! They missed it at my very first ultrasound. Everything still measured right and all of their anatomy is good however I am still worried that I have not eating well enough or drank enough up until this point! I am afraid that the increase in water and an better diet won’t make a difference if something ends up being wrong!

  • Denise says:

    22 years ago, I delivered Mono Di girls who suffered a TwintoTwin Trans. There was an 11% discrepancy, but today they are happy and healthy college grads. Good luck to all future moms who hear this news!!

  • Jessica Villanueva says:

    Im having mono di twin girls scared to death of all these complications. Im only 18 weeks and 2 days idk what to expect

    • Adrian Purnell says:

      Do not stress! You can’t control what goes on, I have recently given birth to mono-di boys and I did everything just right and they came at 32 weeks. I also ruptured at 29 weeks and had to stay in the hospital until I Gave birth. You don’t have control of your body anymore I am sorry to tell ya. Lol I’m sure whatever you have done up until this point is GREAT! Don’t stop now, and don’t over think it. Enjoy the process.

    • Jenn says:

      I just found out I’m having mono di twins. I’m not going to lie I am slightly freaking out. We have two boys 5&3. Any words of advice?

      • JaTarra W. says:

        Don’t stress it! I was told to drink tons of water, but eat normal! I only gained 40 pounds with them both. Water is definitely the key for no cramping! I was dehydrated and I camped so bad they felt like contractions! lol

      • JaTarra W. says:


      • trevor says:

        hang in there were also having mono di twins and I’m freaking out too although I’m starting to feel alittle better…

    • JaTarra W. says:

      Expected the best! Try not to stress!!! You can do it!!

  • Stacey says:

    Just found out via early ultrasound that we’re having mono-di twins! We already have a set of mono-di twins (now healthy 4 year old boys) and never thought we would be so blessed to have another set!

    • Brian says:

      Hi Stacey! My girlfriend and I are expecting for the first time and they are Mono Di Twins, Im very happy that you are going on your 2nd set you’re clearly super woman in disguise lol. But since you’re a vet, do you have any advice for my girlfriend on staying healthy and having a natural birth?

    • Tamira Samuel says:

      Wow! We have a mono di set and pregnant again too early to see.

  • Raven says:

    I’m expecting Mono-Di Twins Boys. This is my first pregnancy. As of now they are healthy and I pray they stay this way till my due date in Aug. Good luck to everyone else

  • Siri says:

    I am 26w4d with MCDA boys. Since 22w, the doctors started close monitoring by weekly scans as they noticed twin B is getting less blood flow than twin A and there was 100gms weight difference between them.

    Until now both are gaining weight consistently and growing well despite the blood flow discrepancy. My OB said so far they are growing well, but we need to watch carefully.

    However the frequent doctor visits, scans, discussions on preemies and NICU stay are very stressful and making me nervous.
    Has anyone had selective growth restriction, but still managed to deliver healthy babies.

    • Fah says:

      I’m 23 weeks now and going through the same situation. I’m scared out of mind. I have been searching to see if anyone has experienced this situation. Please let me know how you are making out.

  • JaTarra W. says:

    Hello to everyone, I just want to say be encouraged and stay encouraged! Believe in Gods reports and not the doctors!!! I’ve successfully delivered mono di twins on November 1st 2017. It was a journey! First I found out that I had a weakened heart ❤️ muscle then with a couple of weeks I found out that I was pregnant . Within a month I found out that they were twins! Mono di. My doctor ‍⚕️ for this pregnancy wanted me to abort, telling me that I could die and much more! I don’t believe in abortions, and not only that I truly believe in God. This doctor was the worst!! Every time she seen me, she wanted something to be wrong! Then we got another scare, them telling me that the babies lab test came back with extra chromosomes! I did cry then I prayed. So many people prayed! We retested and the results were normal!!!! I’m not going to say that it was a perfect pregnancy but we made it through! Towards the end of the pregnancy (35 weeks and 5 days) they twins started developing tts. They were born 4, 5 pounds, even though while I was pregnant they were almost 7 pounds. One of my dd (dear daughters) lungs had fluid in them and the other needed a little help breathing. I also had a c-section. I had a team of doctors because of my heart ♥️ situation, and when everything was said and done and doctors came to visit, that same doctor ‍⚕️ seemed very upset that everything went according to God’s plan! She made the comment, “well nothing happened, and she looks fine, so I don’t know why we are standing around here”… Even the other doctors looked at her weird! Another thing that that the doctors told me was that they were going to be in the hospital for over a month! I refused to believe them once again, we all left the hospital within one ☝️ week! With them being premature, we did have some scary choking incidents with the youngest/smaller one. Otherwise than that, they are thriving!!!! Only thing that I notice with them being premature is that they learn things one month slower. Of course I don’t care ‍♀️, how ever long it takes, I’m just happy their here and made it! They are now 8 months, both are sitting up without help, eating solids, rolling over, trying to crawl, and talk and weight almost 20 pounds each! God is too good! If he can do it for me, he can do it for you! If you have any questions please feel free to ask! God Bless you all!

    • Konadu says:

      Thanks dear I really need this. Am experiencing almost similar situations

    • Deolinda Garcia says:

      That was very encouraging I’m going through the same situation right now and just been praying bcs I know there’s a God who is a miracle worker. Thank you so much for sharing your experience

  • ambere says:

    Just found out last week I am pregnant with mono di twins! I feel double blessed. I’m 10 weeks pregnant. I am so excited but also scared!!

  • Dawn says:

    My daughter-in-lawnis a mono Di twin and is expecting mono Di twins now. Her first cousins and other cousins on her mother’s side are identical twins. She was surprised to find out she was having identicals herself

  • Raie says:

    I am a mother of mo/di boys..they came at 28 weeks for whatever reason I’m not entirely sure they didn’t have ttts
    or trap sequence ..they were respectively 3lbs 0.7 oz and 2 lbs 11 oz..They only stayed a month and a half in the NICU and are now 5 months 3 months adjusted..And now 12 lbs..They are breastfed and cloth diapered..

  • Margaret says:

    Thank you for this article and thread of comments! I just found out last night at 20 weeks 3 days that I two am having Mono-Di babies! Completely surprised when the u/s tech saw 2 and still in shock! I know all will be okay but it’s still SO new and to find out half way through is just mind blowing. Good luck to all on this journey!!

  • Joan M says:

    We found out during delivery that my twins were mono di. I was a high risk pregnancy due to prior complications with other pregnancies so I was getting ultrasound like once a week. They always thought they were measuring two different placentas. But when it came to the delivery my first twin came out. He was heads down. Then when no placenta followed my doctor jumped into action, breaking the amniotic sac of the second twin and pulling him out by his feet. He was born breech. There was not any time to delay because after my first twin was cut from the placenta my second was no longer receiving oxygen. They are 3 years old now. And a hand full, my twin tornadoes.

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