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What Are Mono Mono Twins?

Mono mono twins are an identical twins who develop in a single amniotic sac and share a placenta. The phrases mono-mono and MoMo are brief for “monoamniotic-monochorionic.” This refers to a single chorion (outer membrane surrounding an embryo) and a single amniotic sac (the bag of waters that accommodates the fetuses). This example could be very uncommon and should trigger threat to the infants because of twine entanglement and different points.

How Mono Mono Twins Kind

Similar (monozygotic) twins develop from a single egg-sperm mixture that splits into two. If the cut up is delayed, normally every week or so after conception, the processes of rising a placenta, chorion, and amniotic sac are already underway. The 2 embryos will then develop inside a single, shared sac, leading to mono mono twins.

Solely about 1% of dual pregnancies are monoamniotic; even fewer are monoamniotic-monochorionic.

Nearly all of monozygotic twins develop with separate sacs, or generally with separate amnions inside a shared chorion (described as monochorionic-diamniotic or MoDi). MoMo infants are all the time an identical twins and are of the identical intercourse as a result of they derive from the identical gene set.


Most twin pregnancies are routinely monitored with ultrasound. Docs search for the presence of a dividing membrane that signifies that the 2 fetuses are in separate sacs.

The dearth of a membrane, or a skinny or imprecise line, might immediate additional evaluation to verify the state of affairs. Ultrasound is the one option to detect mono mono twins.

Mono mono twins are sometimes misdiagnosed within the early weeks of being pregnant when the membrane is so skinny as to be almost invisible. Typically, a later ultrasound reveals a dividing membrane, confirming that twins are literally monochorionic-diamniotic.


Pregnant mother and father of mono mono twins ought to be cared for by a perinatologist (an obstetrician specializing in high-risk pregnancies) or at the least seek the advice of with a physician skilled with mono mono twins. Monoamniotic-monochorionic twins face many potential well being dangers all through being pregnant; their survival price is 70%.

Umbilical Twine Problems

The dual fetuses hook up with the shared placenta through their very own umbilical cords, which provide blood and vitamins that assist them develop and develop. Because the infants transfer round in the identical amniotic sac within the uterus, the cords can cross or press towards one another, slicing off these very important lifelines.

This is usually a life-threatening state of affairs. The longer the cords are entwined or compressed, the larger the danger of injury to the cords—and the larger the danger of dying for one or each infants.

Twin-to-Twin Transfusion Syndrome

Mono mono twins are prone to twin-to-twin transfusion syndrome (TTTS), which occurs when one twin (the donor) basically gives a blood transfusion to a different twin (the recipient). The recipient twin usually receives the vast majority of the nourishment within the womb, leaving the donor twin undernourished (smaller and sometimes anemic).

A physician can diagnose TTTS in any set of twins by analyzing fluid ranges of their amniotic sacs. Nevertheless, the truth that mono mono twins solely have one sac makes a TTTS analysis rather more troublesome. Evaluating the bodily improvement of each of the twins is the one option to diagnose this situation previous to delivery.

Irregular Amniotic Fluid Ranges

Mono mono twins could be affected by amniotic fluid ranges which are both too low (oligohydramnios) or too excessive (polyhydramnios). Low blood provide in one of many twins will result in not sufficient amniotic fluid.

This limits motion, bladder measurement, and general fetal progress, along with reducing the safety from compression of the umbilical twine within the uterus. A bigger than regular blood provide will end in extra amniotic fluid, resulting in an enlarged bladder and the opportunity of coronary heart failure. 

Twin Reversed Arterial Perfusion Sequence

Monochorionic twins are at larger threat of dual reversed arterial perfusion sequence (TRAP sequence). On this situation, one twin’s coronary heart (and generally different components of the physique as effectively) fails to develop and the opposite twin’s coronary heart works for each infants.

The dual and not using a coronary heart can’t survive, and the opposite twin can expertise coronary heart failure as a result of its coronary heart is working so exhausting. Therapy includes both early supply or interrupting the blood provide between the twins in order that the more healthy twin has a larger probability of survival.

Low Beginning Weight

Low delivery weight is independently linked to decreased odds of survival and the next threat for disabilities and well being issues in life. Mono mono twins have 4 occasions the danger of low delivery weight as in comparison with pregnancies through which every fetus has a placenta of its personal.

Preterm Beginning

After 24 weeks, the survival price of mono mono twins is about 75% to 80%. Many mono mono twins expertise life-threatening issues as early as 26 weeks, leading to spontaneous preterm supply or an sooner than deliberate Cesarean part (C-section). Preterm supply is commonly related to quite a lot of different life-threatening situations.

Monitoring and Therapy

Fortuitously, trendy expertise permits docs to watch infants within the womb and monitor the state of affairs. Excessive-resolution ultrasounds, Doppler imaging, and non-stress exams assist to evaluate signs and determine potential twine issues.

Twine entanglement and compression are normally gradual processes, so mother and father and medical caregivers have time to make selections. Some conditions would require shut monitoring of the being pregnant within the hospital. Generally steroids could also be administered to spice up the infants’ lung improvement and enhance their possibilities of surviving exterior the womb.

There isn’t a permitted therapy or process to handle the dangers of mono mono twins. The one decision is the supply of the infants. Because of this all are born prematurely.

Docs should stability the dangers of the infants’ situation within the womb versus the results of prematurity. A C-section is normally really helpful for MoMo infants to keep away from twine prolapse, a state of affairs that happens when the second child’s twine is expelled as the primary child is delivered.

If twine compression happens early within the being pregnant, the infants might not be capable of survive. The chance of twine entanglement and compression is just too nice after 34 weeks, so all MoMo twins are delivered at round 34 weeks (if they don’t seem to be born earlier). One small research discovered that vaginal supply of mono mono twins was protected, however it concerned solely 29 births.

A Phrase From Verywell

Studying that your infants are mono mono twins could be horrifying as a result of further dangers they face. Cautious monitoring can be vital, and so will a assist system that you may rely on to assist handle stress and anxiousness throughout this high-risk being pregnant.

Verywell Household makes use of solely high-quality sources, together with peer-reviewed research, to assist the info inside our articles. Learn our editorial course of to study extra about how we fact-check and hold our content material correct, dependable, and reliable.
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  2. Van Mieghem T, Abbasi N, Shinar S, et al. Monochorionic monoamniotic twin pregnancies. Am J Obstet Gynecol MFM. 2022;4(2):100520. doi:10.1016/j.ajogmf.2021.100520

  3. Vitucci A, Fichera A, Fratelli N, Sartori E, Prefumo F. Twin reversed arterial perfusion sequence: Present therapy choices. Int J Womens Well being. 2020;12:435-443. doi.org/10.2147/IJWH.S214254

  4. Kids’s Hospital of Wisconsin. Beginning defects and anomalies in monochorionic twins.

  5. Lee YM. Supply of twins. Semin Perinatol. 2012;36(3):195-200. doi:10.1053/j.semperi.2012.02.004.

  6. Khandelwal M, Revanasiddappa VB, Moreno SC, Simpkins G, Weiner S, Westover T. Monoamniotic monochorionic twins—can they be delivered safely through vaginal route? [9]. Obstet Gynecol. 2016;127(Complement 1):3S. doi:10.1097/01.AOG.0000483625.92567.88

By Pamela Prindle Fierro

 Pamela Prindle Fierro is the writer of a number of parenting books and the mom of dual women. 

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