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Thursday, July 2, 2020

Monozygotic Twins: Origin and Their Associated Complications

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Children are a bundle of joy. Having one child at a time is amazing; however, having a set of twins is something mind-blowing. Twins are a set of two individuals that were conceived at the same time.

In other words, twins are two people who came from the same pregnancy.

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You probably have wondered why a set of twins look alike, and another set have apparently almost nothing in common asides the fact that they shared the same womb at the same time.

This article will help you figure things out. In the meantime, have you ever heard of monozygotic twins?

Monozygotic twins are twins who carry the same DNA (Deoxyribonucleic acids). DNA generally is what scientists call the carrier of genetic information. This means that what makes you unique as an individual is found in your DNA.

However, in the case of monozygotic twins, they have the same kind of DNA. Although most monozygotic twins carry the same type of DNA, they are never really the same. When it comes to identifying an individual through his/her personality, scientists have proved that there are two ways by which this can be done.

These ways include Phenotypic typing and genotypic typing. Phenotypic typing has to do with all those traits that can be seen with the naked eyes—for example, skin color, hair color, etc. Genotypic typing, on the other hand, has to do with your genes.

How are monozygotic twins formed?

Generally, during conception, a single sperm cell is meant to fertilize only one egg. After fertilization has occurred, a zygote is formed. This zygote can be described as the foundation of birth for any individual. It is from this zygote, after a couple of months, a baby is born.


Back to the first stage of development after fertilization, once the zygote is formed, it proceeds to the second stage of development, which is the embryo stage. It is at this embryo stage that determines if you will have one child, a set of twins or other multiple births.

In the case of twins, at the second stage of the development, the embryo can suddenly split into two embryos. You probably are wondering what happens to the cells in the embryo. Each of the cells of the embryo also will split.

This means that, although you originally had one cell during the embryo stage, if the embryo splits, each of those cells will split, giving you two of everything. Hence, each of these embryos can then go on to begin two separate babies.

Recall that in each cell that was initially formed, there was the presence of DNA. Hence, once the split occurs, the DNA of each of these cells also split. As a result, each of those babies carries the same type of DNA within their cells.

It is safe for us to say that monozygotic twins will have the same type of DNA. This is why monozygotic twins are known as Identical twins.

Monozygotic twins will most likely have the same phenotypic and genotypic appearances. Most monozygotic twins are of the same gender; they usually have the same of everything. For example, hair color, eye color, and so on are always the same.

However, somethings will still be different about them, and scientists attribute this difference to the fact that they stayed in separate amniotic sacs, and as such, this difference can result in some minor changes.

It is these minor changes that parents often use to distinguish between monozygotic twins. According to research, monozygotic twins make almost one-third of all twins.

Although, all births have certain risks and pathological tendencies, when it comes to multiple births, then the pathological risks are significantly greater.

In other words, although it is great to have a set of twins, however, there are certain complications that may arise from their pregnancies.

Some of these complications include:


Twin-to-Twin Transfusion Syndrome (TTTS)

This condition is one of the rare complications that can occur in multiple pregnancies. This syndrome is most commonly seen in monozygotic pregnancies because often, monozygotic twins share the same placenta.

TTTS occurs when there is an imbalance in the amount of blood that is being shared with each of the babies. Most monozygotic twins share the same placenta as well as the same blood vessels that supply both nutrients and oxygen to them.

Sometimes, due to unknown causes, one of the twins (often referred to as the donor twin) gives out much more blood carrying oxygen and nutrients than he/she receives to the other twin (often referred to as the recipient twin).

Once this occurs, the donor twin can risk suffering from the inadequate blood supply, nutrient deficiency, stunted growth, or in some worse cases, organ failure, and possible death.

On the other hand, the recipient twin receives excess blood(much more than it is needed), which will lead to the heart of the baby to overwork itself, leading to several cardiac complications and teratologies.

Monozygotic Twins

Twin Reversed Arterial Perfusion(TRAP) sequence

This is another rare medical complication that can occur in monozygotic twins. This condition is said to occur when the cardiac system of one of the twins is responsible for pumping blood to both children.

In this condition, the twin that ends up being the one to supply blood to both of them is known as the ‘pump twin.’ Once this occurs, the heart of the pump twin becomes overworked (because it is doing the job for two).

On the other hand, the other twin that receives the supply without work (also known as the acardiac twin) will either have no heart or have one that is malformed.

Also, the acardiac twin may likely not develop completely, leading to the lack of hands, legs, or a head.

Twin Embolization Syndrome

This is another rare complication that often occurs following the death of one of the twins in-vitro. The type and extent of damage done to the surviving twin depend on the gestational age of the twins.

If one of the twins dies at the early stage of the pregnancy, the other twin will suffer from atresia and tissue loss.

However, if any of the twins die towards the second trimester of the pregnancy, because the heart is already formed, it will result in the other twin developing certain conditions such as tissue infarction.

Once the tissues begin to break down, it forms thromboplastic materials. These thromboplastic materials can enter into the circulation of the other twin and, as such, result in disseminated intravascular coagulopathy.

These emboli can go on to block the flow of some organs in the body of the living twin, including the kidneys, the heart, and the brain resulting in several complications.


Although the causes of these complications are not clear, however, some scientists have speculated that they can be as a result of environmental and genetic conditions as well as lack of adequate drug(s).

In conclusion, monozygotic twins are a set of babies that are born from the splitting of one embryo to form two separate embryos.

These sets of twins are seen to have the same DNA and as such, have the same genotypic and phenotypic features, however, because they were formed in different amniotic sacs, they will have some other minor differences.

If you know you are having monozygotic twins, you must endeavor to follow your doctor’s instructions strictly.

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Deborah Akinola
Wirter, poet and public speaker
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