It’s easy to conjure up a mental image of conjoined twins, but what do you know about them beyond how they look? There’s much to learn about these rare siblings and the extraordinary way in which they live their shared life. Indeed, these 20 eye-opening facts are a great place to start.
20. There are multiple theories as to how conjoined twins form in the womb
Evidence suggests that conjoined twins come from the same egg, and the process malfunctions before it can split into two separate embryos. So, the halves of the egg develop separately to create two babies, but they never detach from one another. However, there have been other theories as to how this rare situation can arise.
Some experts previously believed in embryo fusion as opposed to fissure. As such, they thought that the fertilized eggs would separate as they were supposed to. But as each embryo’s stem cells naturally sought to connect with other similar cells, they’d latch onto the other twin – creating a conjoined pair. Nowadays, though, it’s largely thought that the egg fails to split in the first place.
19. The name “Siamese twins” has historical roots
You may have heard conjoined twins referred to as Siamese twins, and there’s a reason for that. The name derives from Eng and Chang Bunker, who were born in Siam – present-day Thailand – in 1811. A patch of flesh on their chests connected the brothers, and they appeared in circus shows worldwide thanks to this fact.
The Bunkers ended up settling in the United States, where they married a pair of sisters and fathered a whopping 21 children in total. The brothers were both businessmen and farmers until they died in 1874. Their international acclaim earned them the Siamese twins nickname, and this would be used for years to describe other conjoined twins. Nowadays, though, the phrase is considered passé, as babies are born like this around the world.
18. Conjoined twins don’t have a high survival rate
Parents expecting conjoined twins will likely receive a bleak prognosis from their doctors, and that’s rooted in very low birth rates in babies of this kind. Between 40 and 60 percent of all conjoined twins are stillborn, according to reports. And those who survive birth still have a minimal chance of making it much longer than that.
Those same studies found that roughly 35 percent of conjoined twins will die within 24 hours of their delivery. That leaves a very small chance for pairs to make it past their first day of life. And the overarching survival rate for conjoined twins falls within the range of 5 and 25 percent.
17. Conjoined twins are either symmetrical or asymmetrical – and the latter is often fatal
Symmetrical conjoined twins develop similarly to detached twins. Each one has the organs, skin and tissue they need to live separately from their other half. That’s why doctors have more success splitting symmetrical pairs – the two have all they need to live independently of one another.
Meanwhile, asymmetrical pairs don’t have an equal distribution of bodily resources – one will be well-developed, while the other is small and immature compared to their twin. In many cases, the latter baby relies on the former for its nutrition. And the second baby will often be unable to survive on its own or will threaten the life of its healthier twin, so medical professionals may remove it to save one of the babies.
16. There’s a one in 200,000 chance of having conjoined twins
It’s not that rare for someone to give birth to twins; there’s a one in 83 chance that an American woman will get pregnant with a pair of babies, according to Raising Multiples. But multiple births become increasingly rarer as you add more infants to the mix. For example, the organization adds that a triplet occurs once in every 6,889 pregnancies, while quadruplets appear only one time out of 571,787.
Conjoined twins are slightly less rare than pregnancies with more than three babies. One in every 200,000 births results in a pair of this particular type of twins, Science Daily notes. And, as we know, the survival of such pairs is unfortunately rare.
15. The first successful surgery to separate conjoined twins happened in 1955
It has been less than a century since the first surgery to split conjoined twins from one another. The pair in question was a craniopagus set – meaning their bodies met at the skull. But with the help of a support team, neurosurgeon Harold Voris at Chicago’s Mercy Hospital decided to take on the pioneering procedure.
Voris’ 1955 surgery on the conjoined twins resulted in a successful separation of two sisters. Furthermore, both survived the operation and went on to have long lives. As of 1963 reports revealed that the larger twin had gone on to develop along with her peers. The smaller girl had permanent impairments, but she nonetheless survived long-term after the procedure.
14. Conjoined twins need procedures to prepare them for separation surgery
It’s not as easy as wheeling conjoined twins into an operating room for their separation surgery. Instead, it takes quite a bit of time for experts to prepare the siblings for their procedure. One way that doctors ready their patients’ bodies to detach from one another is by expanding their skin, according to the Children’s Hospital of Philadelphia.
The procedure makes sense if you think about it; conjoined twins are born as one, and their bodies have adapted to their unique form. So, when doctors operate to remove them, there won’t be enough tissue to cover the open wound. As such, they insert expanders to stretch the twins’ skin – creating enough tissue to cover surgically created openings post-op.
13. Not all conjoined twins have received fair treatment from doctors
Most of us see conjoined twins in the news when they undergo successful separation surgeries. But not all sets of siblings get a fair shake, and this was especially true in the past when experts knew less about them. For instance, Russian-born twins Masha and Dasha Krivoshlyopova were taken away from their mother, who thought that her girls had died during their delivery.
Dasha and Masha’s bodies met at the spine, where they melded at a 180-degree angle. They had a sole blood system between them, and each girl had one leg. Their unique silhouette led doctors to wonder how one sister would feel if they affected her twin’s side. As a result, they underwent years of experiments before returning to reality and living for 53 years.
12. Conjoined twins are always identical
Twins mainly come in two varieties: fraternal and identical. Fraternal twins occur when a woman’s body releases two eggs at once, and both are fertilized by sperm. Meanwhile, identical twins form when a single egg joins with a sperm before splitting in half to create two of the same embryo.
We know that conjoined twins likely form from a single embryo as well, which would help to explain why all sets of conjoined twins are identical. That means they have the same physical features and, of course, they are the same sex, too.
11. Separation surgeries can be contentious
It may seem as though a separation surgery would be a no-brainer, but it’s not a routine procedure. In some cases, one twin might die, and in others, the weaker baby might have to perish in order to save their stronger counterpart or both will lose their lives. And it’s up to the parents to make this impossible choice.
In one particularly contentious case in 2000, parents Michelangelo and Rina Attard didn’t want doctors to separate their daughters Grace and Rose. Doing so would save the former, as the latter depended on her heart and lungs to survive. However, the split would end the weaker twin’s life. The courts eventually got involved, and they ruled that the surgery should proceed. As a result, the operation – which occurred at St. Mary’s Hospital in the English city of Manchester – allowed Grace to lead a healthy, normal childhood.
10. Conjoined twins are most commonly connected by the heart, liver and intestines
Of course, every set of conjoined twins is different. For all of their uniquities, though, experts have found the common places at which most conjoined twins’ bodies meet, according to CNN. Most often, they’re thoracopagus – meaning they join at the heart, liver and intestine.
The second-most common type of conjoined twins are omphalopagus sets who meet at the liver, intestine and biliary tree, the publication adds. Those who join at the spine, rectum and genitourinary tract are pygopagus twins, while ischiopagus pairs meld at the pelvis, intestine, liver and genitourinary tract. The least common meeting place is at the brain and meninges, and this very rare class of conjoined twins are called craniopagus.
9. Doctors can diagnose conjoined twins early in their mother’s pregnancy
Prior to ultrasounds and prenatal checkups, some moms undoubtedly gave birth to conjoined twins with no idea of their babies’ condition. Today’s technological advancements have helped doctors diagnose conjoined twins much earlier on, thanks to the scans that give them a clear picture of what’s happening in the womb.
Doctors can begin to assess conjoined fetuses at about 18 weeks into gestation, according to the Children’s Hospital of Philadelphia. They can analyze ultrasounds to pinpoint precisely where the babies’ bodies have meshed together. And with that information in mind, they can determine whether or not the twins will be separable by surgery or not.
8. Twins who share a heart cannot normally be separated
Early on, doctors can assess the cardiovascular situation of a set of conjoined twins. They perform a fetal echocardiogram, which allows them to see the heart’s structure and function long before the babies arrive. This test is key in understanding the pair and their options, as it will show if they share a heart.
The fetal echocardiogram reveals if conjoined twins have a single heart, and it can also show where the connection between the babies and their organs takes place. If this shows up, though, there’s bad news for parents: they most likely will not be able to separate their twins. Nevertheless, a number of siblings worldwide have been successfully separated despite sharing parts of the heart.
7. The fastest ever operation to separate conjoined twins lasted 45 minutes
Some surgeries to separate conjoined twins are arduous procedures that last for hours. But there are simpler cases that require much less time, too. One such operation took place in 2003 at Great Ormond Street Hospital in London, England. And this speedy separation was conducted by a pair of surgeons called Edward Kiely and Lewis Spitz.
Spitz and Kiely carefully separated Jannat and Zainab Rahman – twins who shared a liver and whose bodies met at the abdomen. Apparently, the procedure to detach them was much simpler than it sounds and took the experts a mere 45 minutes to complete. At the time, The Guardian deemed the surgery to be the fastest ever operation of its kind.
6. Not all separation surgeries are advisable or survivable
Surgery isn’t an option for all conjoined twins, and it’s not always a safe bet. Iranian-born Laleh and Ladan had always dreamed of living separate lives, but countless surgeons had told the sisters that their particular situation was an inoperable one. So, they lived into their 20s attached at the head, until they saw a news story about a Singaporean doctor who had successfully split 11-month-old twins who had a similar setup.
Finally, the Bijani twins finally got the news they wanted. Surgery was an option, thanks to imaging that showed the inner-workings of their brains. But the procedure didn’t go as planned since the models failed to show a major vein shared between the women’s skulls. So, after hours of surgery, the doctors cut the vein in a last-ditch effort to split the twins, but both sadly died within hours.
5. The longest-living set of conjoined twins died in 2020
For years, Chang and Eng Bunker held the Guinness World Records title as the longest-living set of conjoined twins in history. However, the brothers who inspired the name “Siamese twins” wouldn’t maintain their record forever; another pair of siblings who idolized the Bunkers would take their spot in July 2014.
The Bunkers lived from May 11, 1811, until January 17, 1874 – making them 62 years and 251 days old. On July 4, 2014, though, Ronnie and Donnie Galyon turned 62 years and 252 days old, and this pushed them ahead of the world-famous twins from the 19th century.
4. If one twin dies, the other won’t survive long on their own
Conjoined twins may be two separate people but, at the end of the day, they do share their body. So, if one of the pair dies, the other may survive for a short time, and perhaps even longer if a separation is possible. But if the twins are adults and conjoined, then one twin’s death will quickly cause the other to pass, too.
In the case of the Krivoshlyopova twins, Masha passed away on April 17, 2003, ahead of her sister Dasha. Doctors told the surviving twin that her sister had just fallen asleep, but the truth was that she had died, and the toxins from her decomposing body would eventually poison Dasha’s bloodstream. This wasn’t a unique situation, either; many conjoined twins sadly perish in this way.
3. The majority of conjoined twins are females
Studies have attempted to explain why couples conceive a boy or a girl. For example, one which was published by Victor Grech at the University of Malta and Gwinyai Masukume from the University of the Witwaterstrand found that a baby conceived in the middle of a woman’s fertile period is probably a girl. At any other point, the bun in the oven is more likely to be a boy. And experts have noticed some patterns when it comes to conjoined twins, too.
More male twins conjoin in the womb than female twins do, but it’s rarer to see baby boys make it past this point. Girls are reportedly three times as likely to survive childbirth than their male counterparts. As such, the majority of conjoined twins – a whopping 70 percent of them – are females.
2. Some twins can hear each other’s thoughts
Tatiana and Krista Hogan came into the world connected in more ways than one. They, of course, shared a physical connection as they were born attached at the head. But their brains also had an internal connection at the thalamic bridge – a link that gave them shocking capabilities.
Krista and Tatiana can apparently experience what the other one touches or tastes. The twins can also commandeer control of their sister’s limbs. And, perhaps most interestingly, Tatiana can peer through Krista’s eyes. It works both ways, although Krista can only see out of one of her sister’s peepers.
1. Surgery success has improved over the years, but the procedure is still rare
The mortality rate related to conjoined twins’ separation surgery depends on how their bodies intertwine. For example, those fused at the base of their spine reportedly have a 68-percent survival rate. Meanwhile, those who share a heart that’s specifically fused at the pumping chamber have never been split successfully, according to The Herald.
Surgery success rates have improved as time has gone on, but the procedures remain a very rare medical treatment. The rates of survival are pretty good, though: at least one twin will apparently make it through surgery in three out of four cases.