Clinical Applications Column

by Jennifer Hoar RN

Labour and delivery RN for 20 years in Ottawa.

Citation: Hoar, J.  (2025). The risk that is mono/mono twins! Clinical Applications Column. Canadian Journal of Nursing Informatics, 20(3). https://cjni.net/journal/?p=15311

What are mono/mono twins?

This type of twin pregnancy is quite rare occurring in about 1 in 10,000 pregnancies. Mono/mono is short for mono amniotic (one amniotic sac) monochorionic (one placenta). The babies in this type of pregnancy are always identical.  The babies originate from one fertilized egg that splits after the amniotic sac is already developed.

Imagine two babies swimming around in the same bag of fluid!

One of the biggest risks of this type of pregnancy is cord entanglement. As the babies move around, they run the risk of getting tangled in their own and/or each other’s cords. There is also the risk of cord compression especially as the babies grow and the uterus seems stretched to its limits. Pressure can be put on one or both cords. IUGR (intrauterine growth restriction) is another risk of this type of pregnancy as the babies may struggle to grow appropriately due to potential cord issues or from sharing the same placenta.

Now imagine giving two babies one plate of food!

That is essentially what happens when the twins share the same placenta. TTTS (twin-to-twin transfusion syndrome) occurs when one baby receives more of the nutrients from the placenta and the other gets less. This can cause a significant growth discordance between the babies.

Often, mono/mono twins are delivered prematurely at or before 34 weeks. The risk becomes too great of keeping them inside by that stage. These babies can be delivered vaginally but typically a cesarian section will be chosen as the mode of delivery to lessen the risks of fetal stress.

Managing a mono/mono pregnancy

This type of pregnancy requires careful monitoring. Both external fetal monitoring and ultrasounds should be performed regularly to track the status and sizes of the babies. Steroids should be administered to the pregnant individual for fetal lung maturity. Lastly, the plan should be an early delivery usually by a planned caesarean section. Sometimes the mother is even admitted to the hospital on an antepartum unit for closer monitoring.

If there is evidence of TTTS, there is a surgery called fetoscopic laser surgery that can be done. It involves a laser to cauterize the blood vessel connections in the placenta. It is meant to fix the imbalance. However, this surgery needs special consideration depending on gestation, the severity of the imbalance and the availability of an expert.

Support through informatics

This type of pregnancy requires careful, technology-assisted monitoring:

Informatics in care planning: Electronic health records (EHRs) allow nurses and providers to track fetal monitoring results, maternal assessments, lab values, and interventions over time. Alerts and decision-support tools in the EHR can flag trends, such as changes in growth curves or concerning heart rate patterns, that may require urgent action.

Interprofessional communication: Informatics tools such as shared care dashboards and secure messaging platforms help nurses, obstetricians, neonatologists, and maternal-fetal medicine specialists coordinate care across settings.

Patient education technology: Mobile apps, patient portals, and educational videos support expectant parents in understanding the complexity of a mono/mono pregnancy, preparing them for NICU admission, and reinforcing safe self-care practices.

Even with close monitoring…

The overall survival rate of mono/mono twins is around 70%. With aggressive monitoring and early delivery, this rate can increase to 90%. If one of the twins die in utero, the surviving twin has about a 40% chance of some sort of brain injury. There is a small risk that this type of twins can also be conjoined (about 1%), if there is an incomplete separation of the embryo early in development.

The typical outcome, a short stay in NICU

As these babies are typically born prematurely, there is usually a stay in NICU. Until the babies put on some weight, maintain their temperatures and blood sugars and can feed regularly and breathe on their own, they will likely be in a NICU and closely monitored.

In the NICU, informatics systems play a vital role in ensuring safe and efficient care:

Bedside monitors continuously track heart rate, oxygen saturation, temperature, and respiration, with data fed directly into the EHR.

Nursing informatics tools help manage medication dosing, nutritional support, and feeding schedules, reducing error and ensuring precise documentation.

Analytics dashboards allow NICU teams to evaluate trends in weight gain, blood glucose, and respiratory function to individualize care plans.

Interestingly enough, if there was TTTS present the bigger baby tends to need more help, while the smaller baby usually thrives. The bigger baby is so used to being well supplied that it struggles to thrive on its own. While the smaller baby who used to have to fight for everything it got, no longer must fight.

References

Crider, C. (2025) Mo/Mo Twins: Definition, Risks and More, Healthline. https://www.healthline.com/health/pregnancy/momo-twins

Monoamniotic Twins, Wikipedia. https://en.wikipedia.org/wiki/Monoamniotic_twins

You’re Expecting Twins, Now What?  Sunnybrook Information for Families. https://twincentre.sunnybrook.ca/for-families/

Mayo Clinic Staff. (2022) Conjoined Twins. https://www.mayoclinic.org/diseases-conditions/conjoined-twins/symptoms-causes/syc-20353910