Understanding Conjoined Twins: Full Guide & Common Questions

Conceiving conjoined twins is an extremely rare event, and there are many unanswered questions surrounding this distinctive type of multiple pregnancy. However, scientists have acquired considerable understanding about it over time.

Can conjoined twins be different genders? No, conjoined twins cannot be different genders. Conjoined twins develop from one fertilized egg that did not split all the way. Since they come from just one egg, they will always be identical and of the same gender, just like with other identical twins.

Conjoined twins face complications most of us will never know, but science continues to help us understand more about how they develop and how they live.

Understanding Conjoined Twins

It’s very unlikely that you’ll ever conceive conjoined twins, but it’s still fascinating to understand how they are created and how they live outside of the womb.

How Do Conjoined Twins Form?

Conjoined twins form when one fertilized egg attempts to split but does not completely separate. It stays connected at a point, and that’s where conjoined twins connect.

There is also a theory that conjoined twins form when two identical twin spheres fuse together in the womb. Again, this will create two people who are connected.

Are Conjoined Twins Always Identical?

Yes, conjoined twins are always identical. They come from the same egg, so they have to be the same gender.

Conjoined Twins Types

  • Thoraco-Omphalopagus – These conjoined twins are connected at their chest or stomach.
  • Thoracopagus – Thoracopagus conjoined twins are connected at the thorax.
  • Omphalopagus – These twins are joined at the stomach.
  • Heteropagus – Heteropagus twins are also called parasitic twins and are very rare. This type of twinning occurs when one of the twins passes away but remains connected to the surviving twin.
  • Craniopagus – As the name implies, craniopagus twins are joined at the head or cranium.
  • Rachipagus – These twins are joined at the column of the vertebrae.
  • Parapagus – Parapagus twins are connected at the pelvis, and they are side to side.
  • Pygopagus – Pygopagus twins are connected at the bum.
  • Ischipagus – These twins are facing each other and connected at the pelvis.

What Are the Odds of Having Conjoined Twins?

Only around one in 200,000 births result in conjoined twins, though that is the rate for live births. Conjoined twins can be stillborn. The odds of having them survive the pregnancy and the birth are very rare.

How Rare Are Conjoined Twins?

Conjoined twins are extremely rare. Only one percent of identical twin pregnancies result in identical twins, and identical twin pregnancies themselves are not extremely common. 

How Many Conjoined Twins Are There in the World?

While exact numbers of conjoined twins worldwide are hard to find, 200 sets of conjoined twins are born each year. However, 50 percent will not make it until their first birthday.

How Many Conjoined Twins Are Born Each Year?

Two hundred live births of conjoined twins are reported each year.

Why Are Most Conjoined Twins Female?

There’s no explanation as to why most conjoined twins are female, but they definitely are. The ratio of females to males is 3 to 1.

How Are Conjoined Twins Separated?

Conjoined twins are not always separated because it’s sometimes not possible. To separate conjoined twins, it has to be determined what organs they are sharing and if they can live when separated. 

If separation is an option, then it requires surgery by a highly skilled doctor.

How Do Conjoined Twins Walk?

Conjoined twins walk differently depending on where they are connected. Twins who are facing each other will walk differently than twins who are attached at the head. 

When each twin controls one leg, they have to learn how to coordinate their movements to walk. If twins have four legs with two attached in the middle, they will have to work to move the middle leg at the right time to walk. 

How Do Conjoined Twins Use the Bathroom?

How conjoined twins use the bathroom depends on where they are connected. If they don’t share a bladder or colon, one will simply be in the bathroom with the other one while they use it.

Twins who are connected in places that make movement difficult may opt to use a bedpan instead.

Can Conjoined Twins Share a Brain?

Though it is extremely rare for conjoined twins who share a brain to survive, it can happen.

A pair of conjoined twins in British Columbia share a neural bridge that allows them to share a brain, know each other’s thoughts, and see out of each other’s eyes. 

Can Conjoined Twins Get Pregnant?

There are not widely documented cases of conjoined twins getting pregnant. Though it may be possible, it would be extremely difficult to maintain a pregnancy while conjoined.

Can Conjoined Twins Be Prevented?

Conjoined twins cannot be prevented because we still don’t know what causes them. 

Conjoined Twins’ Life Expectancy

The oldest living conjoined twins made it until 68 years old and died in 2020.

Though there doesn’t seem to be an average life expectancy, most conjoined twins die earlier than other people. However, some have defied the odds and lived into their 60s.

Do Conjoined Twins Die at the Same Time?

Conjoined twins tend to die within hours or days of each other. If they can be separated in time, one twin might be able to make it, but it’s unlikely that this will happen.

If they could have been separated safely, that would have happened while they were living. When the first dies, the other will die due to blood issues or infection.

Rare Types of Twins

Conjoined twins are extremely rare, but they are not the only rare type of twins.

Polar Body Twins

Polar body twins are rare because the way they are conceived is a mix of identical and fraternal twin conception. Though they come from one split egg, the eggs are then fertilized by different sperm.

This means they don’t have identical DNA like identical twins, but they also don’t have as low a rate of common DNA as fraternal twins. They have about 75 percent of their DNA in common.

Mo/Mo Twins

Monochorionic/monoamniotic twins, also known as mo/mo twins, are an extremely rare type of identical twins that share a chorionic sac and an amniotic sac.

That means there is no membrane separating them, and they can actually knot their umbilical cords together, resulting in tragedy. 

Mo/mo twin pregnancies have to be monitored closely, and they are always delivered well before 37 weeks.

Final Thoughts

Twin pregnancies and births are unique, and conjoined twins add even more unknowns to the process. Fortunately, we know more now about this special type of twinning than we did in the past.