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Mono Mono Twins: Facts and Information

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Twins are caused when the fertilised egg splits in two early in your pregnancy. In extremely rare cases, the egg can split far later than normal, which results in your twins sharing a placenta, and also sharing their amniotic sac.

This is called Monoamniotic-Monochorionic twins, (which literally means they share the same amniotic sac and placenta,) mono mono twins, or sometimes even mo mo twins.

Because both of your twins are sharing the same space, with no barrier between them, mono mono pregnancies carry considerable risks for your babies, and require incredibly careful monitoring to make sure that everything is all right.

Unfortunately, even discovered early, momo twins survival rate is quite low, with an in-utero mortality rate of around 50%, because of risks like cord entanglement and twin to twin transfusion syndrome, (TTTS) which we’ll go into below.

What Does This Mean for You and Your Twins?

As soon as it’s discovered that you’re carrying these twins, you should be referred to a doctor specialising in high risk pregnancies, (a perinatologist.)

Because of the risks involved with this type of pregnancy, you’re likely going to need a higher level of care, with far more scans and much closer monitoring as you go through your pregnancy, to catch any complications as they arise.

Bear in mind that both of your twins should be perfectly healthy. Long term, as long as both are born safely it’s not going to affect their health, and they will both go on to live normal, happy lives.

twin matching outfits

Mono Mono Twins Complications

Unfortunately, because they share one amniotic sac, they’re at a far greater risk of fetal death than any other sort of twin pregnancy. Possible complications that can affect your twins include:

  • Cord entanglement: Because both twins are floating in the same sac with nothing in between them, it’s very easy for them to become entangled in each other’s umbilical cords. In the worst case, this can result in a nuchal cord, or an umbilical cord wrapped around the neck of one of your babies. Obviously this poses a pretty big risk. In single pregnancies, nuchal cords generally resolve themselves before birth, but with these twins, this is the main complication that can occur.
  • Cord compression: It’s also possible for one fetus to compress the umbilical cord of the other, resulting in a lack of blood and nutrients being delivered to the other fetus, which can lead to further problems.
  • Twin to twin transfusion syndrome: In any twin pregnancy where the babies share a placenta, there’s a small chance that one baby will receive more blood flow than the other. This leads to one of the twins being larger and healthier, and the other smaller and undernourished. TTTS has 5 stages, from minor through to severe, with associated risks. Thankfully, with new advances in scientific medicine, if TTTS is caught early even the most severe cases can be treated, with a success rate of anywhere up to 90%, which is obviously good.

Because these problems can only be detected by scans, it’s especially important for moms to be that are expecting mono mono twins to be constantly monitored, to enable any situations that occur to be dealt with as best as possible.

Will Having Mo Mo Twins Affect Your Pregnancy?

You’re already having twins, so your babies are likely to have a lower birth weight than single pregnancies. By itself this is nothing to worry about, but twins that share a placenta are even more likely to have a lower birth weight.

Premature delivery is also incredibly likely, as it is with all twins. You aren’t more likely to have an early delivery than any other type of twin birth, but the chance of your twins being born very early, (generally before 32 weeks) is much higher, almost twice as high.

Your doctor will likely recommend that your twins are delivered before their recommended due date, and it’s also a lot more likely that a caesarean section will be recommended, to aid in delivery and lower the possible risk of complications.

If a cord entanglement situation is discovered, it is possible that your doctor will recommend an extremely early delivery, potentially as early as 24 weeks, as cord entanglement is a major risk and this gives them the greatest chance of survival.

TTTS has also recently become treatable, using a technique called laser ablation that strategically severs smaller blood vessels in the placenta to balance the blood flow between your babies. Whilst this sounds scary, it increases the chance of both twins making it to full term from around 10% to almost 70%!

What Can You Do for Your Mono Mono Twins?

Carrying them isn’t normally any different for the mother. It generally depends on the needs of your babies, and can change depending on differing situations.

The most significant change is the frequency of scans and other health and observation checks, which your doctor will perform to make sure that nothing major is happening that could threaten the well being of your babies.

In the worst cases, for example cord entanglement, it’s possible that you could be hospitalized to give your doctor the ability to constantly monitor you, but this is only going to happen in the worst cases.

In general, just look after yourself as best you can and follow any advice your doctor gives you. Get adequate rest, eat healthy, try not to overexert yourself, and don’t worry. Remember that you’re in the best hands possible!

What Does All This Mean?

In the past, learning your twins were mono mono was a massive problem. It meant that you were probably going to lose one, if not both. But with advances in medicine and the far greater level of care we have today, having mo mo twins isn’t the sentence it once was.

Of course, you’re still going to need close monitoring, and it’s natural to worry, but just remember than finding our your twins are mono mono early gives them the best survival chance possible, and in all probability you’re going to be giving birth to a pair of happy, healthy babies! That’s awesome!

Did you have mono mono twins? Maybe you’ve just been diagnosed with a mo mo pregnancy and want to ask our advice, or even offer some. Whatever it is, we’re here, and whatever you need, let us know in the comments below.


  1. I have 9 year old twin girls. They were mono amniotic twins. I had to see perintologist and have hi definition ultrasounds every two weeks of my pregnancy. I went into preterm labor at 30 weeks, but my labor was stopped and I ended up on hospitalized bed rest for close monitoring. I ended up being induced at 37 1/2 weeks. My girls were very healthy at 5 lbs 4 oz and 6 lbs 2 oz. I realize how blessed we were to have such healthy high risk twins!

  2. I am at 17 weeks with mono twin girls. Was sent to a high risk ob to make sure that things run smoothly. But I do not feel comfortable with this new Dr. He pretty much stated that most of the possibilities for complications is something that I’m going to have and that i am no longer allowed to see my normal ob, or the hospital that I have just 8 blocks from my house. So am wondering if anyone else has been in this situation?

  3. My mo-mo twin girls are now 25 years old. Back when I was pregnant, my ob explained the risks to me, but I really didn’t have any concept of how rare this type of pregnancy was. It’s probably a good thing that I didn’t have access to the internet like we do now, or I would have freaked myself out.

    My pregnancy was pretty uneventful. I had ultrasounds once a month (this was at a teaching hospital, so I always had large groups of students looking on…fun times!) After the 3rd trimester the fetal heartbeats were monitored twice a week. The girls were born by cesarean at 38 weeks and weighed 5 lbs 4 oz, and 6 lbs 3 oz.

    I realize how incredibly blessed I am to have these two healthy, amazing daughters of mine. I want anyone reading this who is pregnant with mo-mo twins to know that you don’t need to panic. You too can have 2 healthy babies. I did it 25 years ago, and medical technology has come a long way since then.

  4. My sister and I are mo-mo twins. When we were born in 1963 the doctors delivered my sister and she was extremely red and full of blood. When I came out I had very little blood and no heart beat, clinically dead they called it. They did immediate CPR and blood transfusion and saved my life. Once the amniotic sac was delivered they took pictures of it because it was all snarled and twisted. That is when they discovered that we each had our own umbilical cord and it was attached to only one amniotic sac. They were quite surprised. Somewhere there is a book with the photos and story of it all. We were very lucky to have the doctors we had that didn’t give up on us. We were premies, just over 7 months and weighed 4 lbs 8 oz. and 4 lbs 12 oz. When we were toddlers I was left handed and she was right. We always thought we were unconnected Siamese twins. My mother was told April 1st that she was to have twins but that is all they knew at the time. She was quite upset since she was a petite 5′ 4″ at 100 lbs.

  5. Cord entanglement happens very early on in momo pregnancies, so only NST decels or other complications will create a reason to deliver as early as 24 weeks. 32-34 weeks is the goal. If you are pregnant with momo twins, join a support group, like on Facebook!

    My momo boys are 1 year old today. ūüôā

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