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What to Expect When You're Expecting Mono/Mono Twins

Updated: Oct 15, 2021

Your First MFM Appointment

Once your OBGYN sends a referral to MFM (or perinatologist), they will schedule you for a detailed ultrasound, typically between 10-14 weeks gestation. This ultrasound will be to check for a dividing membrane, which will determine if your identical twins are either monochorionic/diamniotic (also known as mono/di or modi - a dividing membrane is present: babies are sharing the same gestational sac but have their own separate amniotic sacs) or monochorionic/monoamniotic (also known as mono/mono or momo - no dividing membrane found: babies are sharing the gestational and amniotic same sac). A membrane is best found between 10-16 weeks, but can be found as late as 20 weeks gestation.

Your Monitoring Plan: Weeks 16-24

Once you find out what kind of identical twins you're having, your MFM doctor will go over how your pregnancy will be treated. Up until viability (24 weeks), mono/di and mono/mono twins follow the same plan: bi-weekly monitoring for Twin-to-Twin Transfusion Syndrome (TTTS) via ultrasound. This specific ultrasound monitors fetal growth and amniotic fluid levels, as well as performing umbilical artery dopplers. This in-depth monitoring typically begins no later than 16 weeks gestation and will be routine for the remainder of the pregnancy.

Umbilical artery dopplers are performed to ensure that each baby is receiving equal amount of nutrients/blood from the placenta. In some cases, one twin will receive more than the other twin. This is where TTTS comes into play. A brief, easy-to-understand explanation of TTTS can be found here.

In addition to bi-weekly appointments with MFM, you will likely still see your OBGYN. This would occur on the opposite weeks of your MFM appointments, and happen every 2-4 weeks. These appointments are very standard, with the OB checking for heart rates on each twin, measuring the fundal height of your growing belly, testing for protein in your urine, and a blood pressure check.

Important Scans

There are a few important milestone scans that will happen at the MFM during your pregnancy. These scans are the Nuchal Translucency (NT) Scan, Early Anatomy Scan, Anatomy Scan, and Fetal Echocardiogram.

  • The NT Scan measures the pocket of fluid behind the fetus' neck as an initial marker for chromosomal abnormalities, such as Down Syndrome. This scan is typically conducted between 11-14 weeks gestation.

  • The Early Anatomy Scan is conducted at 16 weeks gestation. At this scan, the babies are fully formed but still very small. At this scan the kidneys, bladder, and heart will be checked. It may be difficult to get a good look at the full anatomy of the heart, and is best seen at 20 week the Anatomy Scan.

  • The Anatomy Scan occurs around 20 weeks gestation. At this scan, the entire anatomy of the baby is observed, including a very detailed look at the baby's brain and heart. Because of the level of detail of this scan, it typically takes the longest in duration - approximately 2 hours (1 hour per baby). Be sure to empty your bladder before the scan, and also request frequent breaks if you're feeling lightheaded or nauseous due to being on your back for too long.

  • Lastly, the Fetal Echocardiogram is performed between 22-24 weeks gestation. This is very similar to the ultrasounds you've been attending, but this in-depth scan is specifically to look at the structure and functionality of each twin's heart - looking for any abnormalities in the heartbeat or blood flow.

Your Inpatient Stay

Please note that the following information is specifically related the standard practices used in the United States. Many countries, especially ones in Europe, do not offer inpatient care. Please talk to your perinatologist/MFM doctor about your specific situation.

Your MFM doctor will likely recommend hospital admission for frequent monitoring between weeks 24-28 gestation. Standard delivery for momo twins occurs between 32-34 weeks. The safest method of delivery for momo twins is via cesarean section. This is because of the risk of cord compression due to entanglement, which is almost always seen in mono/mono pregnancies - some cases more severe than others.

The decision for what week you are admitted is based on the recommendation of your doctor, as well as your level of comfort. Meaning, you are entering the hospital knowing that you could deliver these babies via emergency c section the minute you walk in. Because of this, it is important to do plenty of research and also discuss with your partner/family about when you'd be comfortable delivering your babies.

Although this is a standard recommendation in the US, it is also completely optional. Some momo mamas will opt for outpatient monitoring up until delivery. In most cases, mamas will continue to do outpatient monitoring if they have young children at home.

During your inpatient stay you will be monitored via non-stress tests (NSTs), typically 2-3 times per day for approximately 1 hour. NSTs monitor each baby's heart rate. If decelerations (slowed heart rates) are found on either baby and look concerning, your doctor will continue to monitor the babies for a longer period of time to see if the heart rate returns to normal. If one or both babies continue to be in distress, your doctor may choose to deliver the babies.

In addition to NSTs, you will likely receive weekly ultrasounds to check the amniotic fluid levels and the babies' heart rates, and continue bi-weekly scans to monitor for TTTS. Growth scans typically occur every 3-4 weeks.


Based on the babies' growth and the NST scans, your doctor will discuss with you when he/she recommends delivery. As stated, this typically occurs between 32-34 weeks. Due to prematurity of the babies, a NICU stay will be required. However, because of the risk of cord compression/pinching of the growing babies, it is considered safer for the babies to be out than in at this gestation.

NOTE: The Content in this blog is intended to be informative, but is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding your pregnancy. Never disregard professional medical advice or delay in seeking it because of something you have read on this Website.

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