The feeling after you discover that you are having twins is unmatchable. But this feeling of utmost joy and happiness may turn into your worry if you get to know that your twins are sharing not only the womb but the same amniotic sac and placenta. The worry is because it is the rarest case in which identical twins share the same amniotic sac and placenta, and it is also highly risky. This scenario tells that your twins are navigating pregnancy in an incredibly close (and complex) bond. And this situation is called monoamniotic-monochorionic (mono-mono) twins. 

The idea of having twins is really exciting, but having mono mono twins can give you chills down the spine when you think of cord entanglement and preterm birth. If you don’t know what mono twins are, this blog will cover everything that you must know about mono-mono twins. 

How Mono-Mono Twins Form?

Mono-mono twins form in early embryonic development when the fertilized egg gets split later than usual. These twins originate from the same sperm and the same egg. This split happens in the 9-12 days after fertilization. 

In the first 4-5 days, the out membrane which forms the placenta develops. In 7-8 days inner membrane develops, which holds amniotic fluids. 

After 9 days, the embryo splits, and the twins share the placenta and amnion (sac).

It is a rare situation because out of all pregnancies, only 1% of pregnancies are mono mono. 

Diagnosis of Mono-Mono Twins

An ultrasound after 10 to 14 weeks of pregnancy is the best way to confirm the mono-mono pregnancy. Even a transvaginal ultrasound also confirms this type of pregnancy because it gives a clear image of a shared sac confirming mono-mo twins.

Then, the medical providers also opt for a Doppler ultrasound to have a clearer view of umbilical cords because cord entanglement and compression are the biggest risks of mono-mono twins.  

Risks of Mono-Mono Twin Pregnancies

Since both fetuses share the same sac, umbilical cord entanglement is the biggest risk of mom mono twins. 

• The cords can also get compressed, restricting the blood flow and oxygen supply, which is fatal for the fetuses. 

• Twin-to-Twin Transfusion Syndrome (TTTS) is another great concern of mono mono twins. It is a condition in which an imbalance in blood flow between the twins causes one twin to have more blood than the other. 

• Due to higher risk factors, Mono mono twins are delivered early, typically around 32-34 weeks, mostly via C-section. 

• Unequal sharing of the placenta causes Intrauterine Growth Restriction (IUGR), restricting the growth of fetuses. 

• The risk of losing one baby or, in some cases, both is much higher in Mono mono pregnancy than in normal twin pregnancy. 

Most mothers are hospitalized for closed monitoring as the time approaches. Due to all these risks, mono-mono pregnancies require intensive parental care that includes frequent ultrasounds. Medical providers might suggest daily ultrasounds to monitor the progress. 

The delayed split puts both fetuses in the shared life support system (placenta), creating a unique yet challenging experience for the mother.