MoMo Twins - Definition, Diagnosis, and Complications

Introduction

MoMo twins are a unique type of twins who share both the chorionic and amniotic sacs. The term "MoMo" is derived from the phrase monochorionic monoamniotic, which simply means that these twins have one placenta and one amniotic sac. In other words, a MoMo pregnancy involves both babies developing in a single placenta and sharing the same amniotic sac, as the prefix "mono" indicates "one." Monoamniotic twins, on the other hand, are an extremely rare phenomenon where a single fertilized ovum gives rise to identical twins who also share the same placenta and amniotic sac. These twins are exceptionally uncommon, accounting for only one percent of all identical twins and less than 0.1 percent of all pregnancies.

What Are MoMo Twins?

Identical twins that develop in a single amniotic sac and share a placenta are referred to as mono-mono twins, or MoMo twins for short. The term monoamniotic-monochorionic describes this condition, which involves a single chorion and a single amniotic sac. Although rare, this situation can pose risks to the babies, such as cord entanglement and other complications.

Monozygotic twins, also known as identical twins, arise from a single fertilized egg that divides into two. In cases where the division occurs later, typically around a week after conception, the formation of a placenta, chorion, and amniotic sac is already in progress. Consequently, the two embryos develop within a single, shared sac, resulting in what is referred to as mono-mono twins. Approximately one percent of twin pregnancies are classified as monoamniotic. Furthermore, an even smaller fraction falls under the category of monoamniotic-monochorionic twins.

What Are the Various Types of Twins?

• Monochorionic Twins - Identical twins with a single placenta are known as monochorionic twins. This occurs in around 70 percent of identical twin pregnancies.

• Monochorionic-Monoamniotic Twins - They are twins who have the same placenta as well as an amniotic sac.

• Monochorionic-Diamniotic Twins - Identical twins that do not share an amniotic sac but do share a placenta are known as monochorionic-diamniotic twins.

• Dichorionic Twins - They have separate placentas and amniotic sacs. This occurs in approximately thirty percent of identical twin pregnancies. Dichorionic twins include all fraternal (non-identical) twins.

How Are Monoamniotic Twins Diagnosed?

• Twin pregnancies are commonly monitored through ultrasound to ensure proper care. Twin pregnancies are usually identified by doctors during a routine prenatal ultrasound, with the most optimal images being obtained before the 14th week of pregnancy. This is because the structures of the placenta and amniotic sac are most clearly visible during this time.

• Physicians examine the presence of a dividing membrane, which signifies that the two fetuses are contained in separate sacs. In cases where there is no membrane or a thin and indistinct line, additional analysis may be prompted to verify the situation. Ultrasound remains the sole method to identify mono-mono twins.

• During the initial stages of pregnancy, mono-mono twins are frequently misdiagnosed due to the extremely thin nature of the membrane, making it almost invisible. However, a subsequent ultrasound often reveals the presence of a dividing membrane, thereby confirming that the twins are indeed monochorionic-diamniotic.

What Are the Health Risks Associated With MoMo Twins?

Usually, risks already increase when a woman is pregnant with more than one baby. With less room to grow, twin pregnancies usually result in preterm birth. However, monoamniotic-monochorionic twins face additional risks because they share a single placenta and amniotic sac. These health risks include the following.

• Entangled umbilical cords may become wrapped around the babies.

• Compressed umbilical cords that end up in knots and cut off blood supply.

• Reduced blood supply for each baby because of sharing.

• Uneven blood flow stunts growth in the womb, often affecting only one baby, and is also called selective fetal growth restriction (sFGR).

• Rapid transfer of blood from one baby to the other can lead to heart failure and the death of one or both twins.

• Amniotic fluid abnormalities, meaning the babies may have too much or too little fluid.

• Congenital malformations, including defects of the heart, neural tubes, or brain.

• Delays in meeting expected milestones following birth‌.

What Are the Complications Associated With MoMo Twins?

• Problems with Amniotic Fluid: Inadequate amniotic fluid may restrict bladder size and movement, while enough amniotic fluid can cause an enlarged bladder and raise the risk of heart failure.

• Cord Entanglement: Because there is no barrier between MoMo twins, their umbilical cords can become tangled over time. If there are any concerns, this might result in very early twin deliveries and possibly quick death.

• Twin Reversed Arterial Perfusion Sequence (TRAP): This rare condition occurs in about one percent of MoMo pregnancies. One twin develops normally, while the other twin forms without a functioning heart and other body structures. The two are connected by a large blood vessel, and the twin without a heart receives all its blood from the other twin. This puts a significant strain on the twin's heart, increasing the likelihood of heart failure or death as the twin without a heart grows larger.

• Twin-to-Twin Transfusion Syndrome: When the placenta is shared in a MoMo pregnancy, one twin may receive a greater blood volume and nutrients than the other. This might cause problems for both babies and may necessitate monitoring, preterm delivery, or surgery.

How Are Momo Twins Monitored and Managed?

• Modern technology has enabled doctors to closely monitor babies in the womb and detect potential cord problems through the use of high-resolution ultrasounds, doppler imaging, and non-stress tests.

• In cases where cord entanglement or compression is identified, medical professionals and parents have time to make informed decisions and may opt for close monitoring in a hospital setting or the administration of steroids to improve the babies' lung development.

• Unfortunately, there is no approved treatment for mono-mono twins, and premature delivery is the only resolution. Doctors must weigh the risks of the babies' condition in the womb against the consequences of prematurity, often recommending a C-section to avoid cord prolapse.

• Cord compression early in the pregnancy may result in the loss of the babies, and the risk of entanglement and compression is higher after 34 weeks, leading to delivery at around this time.

Conclusion

MoMo twins are a rare and risky type of monozygotic twin who share the same amniotic sac and placenta. The unique nature of their development needs thorough medical supervision throughout their pregnancies and deliveries, to ensure the best possible outcome for the twins and the mother.