If you are an expectant parent, twins are often a happy surprise. But when you learn that your twins are mono mono—or sharing the same amniotic sac and placenta—the news can be both scary and exciting. That was the case for us when we got the news we were having mono mono twin girls.
While mono mono twins are relatively rare, occurring in just 1% of all twin pregnancies, it’s important for you to know what to expect.
Before we get into it, let me first share a crazy story with you.
The “18-Weeks Pregnant” Ultrasound
Our ultrasound technician, Savannah, broke the news to us by saying, “You know you’re having twins right?”
Up until this point, Dave and I knew we were having one baby (from our 7-week ultrasound) AND two weeks prior (during our baby reveal party) we found out we were having a girl.
The word ‘shocked’ doesn’t even describe how we felt at that moment because for half my pregnancy we knew we were having one baby!
Now that Dave and I have almost passed out (thanks Savannah!), all the questions came flooding in…
- What are mono mono twins?
- What are the high-risk complications?
- What are the next steps?
You may be thinking the same things we did, so let’s get to it. Here’s what you need to know about mono mono twins.
What Causes Mono Mono Twins?
Mono mono twins occur when an embryo doesn’t split until after the amniotic sac is formed. This usually happens around the 12th day of development, after the egg has been fertilized and begins to divide.
In most cases, the embryo will split into two separate amniotic sacs within a few days. But in some cases, the splitting process happens slowly, or not at all. As a result, the twins share the same “everything”—which are the amniotic sac and placenta.
What Are Mono Mono Twins?
To reiterate, Mono mono twins are identical twins who develop in a single amniotic sac and share a placenta. You may hear the terms “mono-mono” or “MoMo” which mean the same thing and are short for “monoamniotic-monochorionic.”
This refers to a single chorion (the outer membrane surrounding an embryo) and a single amniotic sac (the bag of waters that contains the fetuses). This situation is very rare and may cause risk to the babies due to cord entanglement and other issues. This is why Mono Mono twins are considered a high-risk pregnancy.
Speaking of risk, it’s important to know the complications that can happen.
Complications Associated With Mono Mono Twins
Because they share the same amniotic sac, mono mono twins are at a higher risk for complications than other types of twins. These risks include:
Intrauterine Growth Restriction
One or both of the twins may experience intrauterine growth restriction (IUGR), which can lead to problems with organ development and low birth weight.
Intrauterine growth restriction (IUGR) is a condition that can affect any baby during pregnancy but is most commonly seen in babies who are born prematurely. IUGR occurs when the baby’s body or organs do not grow as expected. This may be due to problems with the placenta, the mother’s health, or the baby’s genes.
In some cases, medical intervention may be necessary to treat IUGR such as steroid injections. These injections help speed up fetal lung development in order to prepare for an earlier delivery.
Twin-to-Twin Transfusion Syndrome (TTTS)
This occurs when blood vessels in the shared placenta connect the twins’ circulatory systems. As a result, one twin may receive more blood and nutrients than the other, leading to unequal growth rates.
If TTTS is diagnosed early enough, laser surgery is an option to seal off the abnormal connecting blood vessels in the placenta to stop the harmful sharing of fluids. It involves making small incisions in the placenta to allow for better blood flow between the twins. The goal is to hopefully reverse or stop TTTS. However, even with treatment, there is no guarantee that TTTS will not recur.
In very rare cases, one or both of the twins may pass away in utero due to complications like a cord accident, twin-to-twin transfusion syndrome, or IUGR.
Mono mono twins are more likely to be born prematurely than other types of twins. In many cases, spontaneous preterm labor occurs between 26 and 28 weeks. As a result, most of these rare types of twins are born via c-section and spend time in the NICU (Neonatal Intensive Care Unit).
At least this was the case with us.
Our mono mono twin girls were born early at 27 weeks via emergency c-section.
My husband and I made the choice for me to go inpatient at 24 weeks for continuous monitoring. I’m so grateful we did because our nurse caught a cord accident while I was on the monitor which saved both of our girls’ lives!
What To Expect
If you’re pregnant with mono mono twins, you’ll be monitored closely by your healthcare team. You can expect to have more of these things happen than other pregnant mamas:
- Detailed ultrasounds
- Non-stress tests
- Frequent prenatal visits
- Scheduled c-section (usually around 32 weeks)
In some cases, you may be referred to a high-risk obstetrician or perinatologist—a doctor who specializes in high-risk pregnancies.
As for our experience…
Once Dave and I found out at 18 weeks we were having mono mono twin girls, our world completely changed.
I was overseen by a high-risk team at Riverside Hospital where I delivered our girls at.
My OBGYN became “second” in the chain of command. Riverside Hospital called the shots and my OBGYN followed their lead.
We went to ultrasounds every 2 weeks.
After our 18-week ultrasound, I was scheduled routinely every 2 weeks to check the girls’ heart rates and blood flow. The good news is with mono mono twins you get to see your sweet babies MORE often. 🙂
One thing that never came up for me was to take a non-stress test. I’m sure if you are interested or have questions, talk to your healthcare provider about this.
I went inpatient at 24 weeks for continuous monitoring.
If you live in the United States, you have the choice to check inpatient anywhere from 24 to 28 weeks for monitoring your twins’ heart rates and blood flow. I would HIGHLY recommend checking in at 24 weeks and being on the monitor as much as you can (I did this for up to 8 hours a day, sometimes more). The monitor is what saved Lua and Lily Mae’s life.
I understand mental health is important too, but try to monitor your babies as much as possible. If you think about it, it’s such a short period of time to be on the monitor versus a lifetime of love that awaits you with your precious ones.
To Wrap It Up
Dealing with a high-risk pregnancy can be stressful for both moms and dads—but knowing what to expect can help you feel more prepared for what’s ahead.
If you’re expecting mono mono twin girls or boys, keep in mind that while complications are possible, they don’t always occur. With close monitoring by your healthcare team, most babies go on to healthy lives outside the womb.
Until the next post, I’m sending you all the positive parent vibes!
Thank you for being here today!
Do you have anything to add or tips to share for expectant mono mono twin parents? Let us know in the comments below. We could all use a little help along the way. 🙂
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About The Author
Lindsey is a mom of two little miracles, MoMo twin girls, Lily Mae and Lua, plus one amazing older bro, Cody.
“Consider me a ‘blog super nerd’ at heart. I love helping busy parents learn how to blog because it has personally been life-changing for me and my family. Plus, sharing my experience to help others on their twinhood journey is so rewarding!”
She is the founder of Twin Mom Blog Nerd, Content Creator/Co-Founder of the blog Intensive Therapy for Kids, and Co-Founder of The LENN Foundation 501(c)(3) charity that helps children with cerebral palsy (like her sweet nephew, Lenny) receive grants for intensive therapies to thrive. ♥
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