Different Types of Twins | An Amazing Guide To Twins

Unless you have twins in your family, you might not have thought much about the different types of twins there are. You’ve probably heard of identical twins, but did you know there are actually several kinds of twins?

As a twin yourself or just curious about twins in general, you’ve come to the right place. This article will give you a guide to the different types of twins out there. Whether you’re a twin parent wondering how twins form, a twin looking for answers about your own situation, or just someone fascinated by multiples, understanding the differences between identical, fraternal, and other twin types.

You might be surprised to learn about the many different variations or types of twins.

The different types of twins

Of course, despite the shared DNA and upbringing, life experiences can shape children in unique ways. Identical twins can have different hobbies, friends, and personalities. They may share striking similarities, but they are still individuals following their own path in life.

In the end, no matter if they’re identical or fraternal, twins share an extraordinary relationship. They’ll always have a built-in best friend who understands them like no one else can. What an amazing gift to experience the world side by side with your twin!

There are several types of twins beyond just identical and fraternal. The more you learn about twins, the more fascinating they become!

Fraternal twins (dizygotic twins)

Fraternal twins, also know as dizygotic twins, or non identical twins, come from two separate eggs that are fertilized by two different sperm at the same time. This produces two genetically unique children.

Genetically speaking, non identical twins are no more similar that other siblings born at different times.

Although there are genetic differences, non identical twins are still likely to share more commonalities than other siblings born at separate times. This could be due to environmental factors at the time of conception and birth, as well as being raised under the same parenting style.

Fraternal twins are the most common types of twins, with about two-thirds of all sets of twins being dizygotic twins.

Identical twins (monozygotic twins)

Identical twins, also know as monozygotic twins, are conceived from just one egg and one sperm. The fertilized egg splits in half, and two babies of the same sex and with exactly the same genetic information are formed. This is why identical twins have the same physical features.

Monozygotic twins make up about one in three of all sets of twins.

There are different types of identical twins; they are classified according to the stage of fertilization at which the egg splits to form two separate eggs.

Dichorionic diamniotic twins

Dichorionic diamniotic twins (or DCDA twins) each have their own amniotic sac and separate placenta. They are often fraternal twins, but DCDA twins can also be identical twins when the egg has split very soon after fertilization.

Monochorionic twins

Monochorionic twins (or MC twins) have two separate amniotic sacs but share the same placenta. This is the result of the fertilized egg separating after attaching to the wall of the womb.

Monochorionic twins occur in about two-thirds of identical twin pregnancies.

Monoamniotic twins

Monoamniotic twins (or MoMo twins) share the same amniotic sac and placenta. This happens in rare cases when the fertilized egg splits even later than it does in monochorionic twins.

Monoamniotic twins only occur in a very small number of twin pregnancies.

Semi identical twins (sesquizygotic twins)

If twins are classified as identical twins or non-identical twins, then what on earth would determine semi identical twins?

Semi identical twins (or ‘half identical twins’) occur when two sperm fertilize one egg, and that egg splits in two. This results in identical twins with 3 sets of chromosomes rather than two.

Semi identical twins are so rare that only two cases have been reported globally.

Mirror image twins

Mirror image twins are a type of monozygotic twin (identical twin), where characteristics that appear on one side in the first twin appear on the opposite side in the second twin.

For example, in mirror twins, one twin might be right hand dominant while the other is left handed. Even physical features, such as birthmarks, freckles, dimples or cowlicks can be manifested as a mirror image in each twin.

In one study on 8 monozygotic mirror image twin pairs, it was found that the left middle finger pattern on one twin was the mirror image of the right middle finger pattern on the other twin.

In exceptionally rare cases, it has been found that some mirror image twins had internal organs on the opposite side from their normal anatomical positions.

Conjoined twins

Conjoined twins are another type of identical twin that occurs when the separation of the fertilized egg is incomplete. This results in the twins being born with their bodies attached to each other, with the possibility of the two babies even sharing internal organs or limbs.

Another theory suggested that two eggs, previously fertilized separately, fuse together soon after fertilization; however, this is now believed to be inaccurate.

Conjoined twins are a rare phenomenon, occurring once in every 50-60,000 births. Seventy percent of conjoined twins are twin girls. Approximately half of all conjoined twins are stillborn, and an additional one third die within 24 hours of birth.

Depending on how and where conjoined twins are attached to each other, surgery to separate them can range from being somewhat straightforward to extremely complex. If twins are conjoined at the head or share a vital organ, separation surgery is deemed life threatening.

Parasitic twins

Parasitic twins are a type of conjoined twins who are asymmetrically joined. This is a result of an incomplete separation of two embryos in utero. In these cases, one embryo is dominant, at the expense of the other.

The ‘parasitic twin’ is incompletely formed, and dependent on the dominant twin’s organs for survival. In most cases, development stops at a certain stage in utero, and the dominant twin is born with limbs, organs, or other body parts from the parasitic twin attached to them.

Heteropaternal superfecundation (twins with different fathers)

As unbelievable as it sounds, it’s actually possible for twin babies to have two different fathers.

Heteropaternal superfecundation occurs when more than one egg is released in the same cycle, and two eggs are fertilized by two separate sperm during separate acts of intercourse in a short time period.

For more information about superfecundation, you can read BellyBelly’s article Superfecundation | Can A Baby Have Two Fathers?

Irish twins

The term ‘Irish twins’ refers to siblings born less than twelve months apart.

They are technically not twins. Irish twins is a name that originated in the 19th century when Irish immigrant families in the USA did not have access to birth control.

The term is less commonly used today.

The Twin Bond Connection Between Twins

Twins, share a connection unlike any other. Beyond the physical similarities, there is a deep emotional and psychological bond between them that forms even before birth.

The twin bond begins in the womb, where they spend months together developing at exactly the same pace. After birth, they continue to share countless experiences together as they grow up. This creates an intimate understanding of each other that transcends words and connects them in a profoundly unique way.

Some twins describe their bond as being able to sense when the other is happy or sad, even from far away. They may finish each other’s sentences or have special ways of communicating that only the two of them understand. These shared moments help cultivate a lifelong connection that provides friendship, support, and loyalty like no other.

Of course, the twin bond varies for each pair. Identical twins often report an especially strong emotional connection, but all twins can develop profound bonds. Nurturing twin connection with quality time together, open communication, empathy, and mutual support will help strengthen this lifelong relationship.

While the twin bond may change over the years, at its core remains a deep affection and understanding that comes from sharing life’s journey together.

For more interesting facts about twins, you can read BellyBelly’s article Pregnant With Twins? | 8 Interesting Facts About Twins.