Extraordinary Twins follows a couple from Idaho, whose daughters are joined together at the sternum – so what causes conjoined twins?
How difficult is it to separate them, and how many survive?
Here’s everything you need to know.
Read more: This Morning viewers divided over conjoined parents’ tough decision
Extraordinary Twins on ITV1
A two-part documentary following Nick and Chelsea from Idaho.
Their twin daughters Callie and Carter are united at the sternum.
The programme meets the family as the twins approach their fourth birthday.
The parents face the agonising decision of whether to put them through complex surgery to separate them.
To help them make this fateful decision, the family heads on an emotional journey to meet other conjoined twins and their parents.
They meet 20-year-old Carmen and Lupita, who featured in Channel 4’s Two Sisters, One Body last year.
They have remained joined.
Eighteen-year-old twins Sohna and Mohna from Amritsar in India remain joined together – and are training in electrical engineering.
Meanwhile, we follow the risky surgery involved in separating Turkish twins Yigit and Derman at Great Ormond Street Hospital.
Skilled surgeons face the intricate task of separating their heads.
Extraordinary Twins on ITV1 – who narrates?
Sheridan Smith narrates this fascinating and moving documentary.
The actress and singer, 40, has previously narrated Cilla: The Lost Tapes, Dispatches and Used Car Wars.
She most recently appeared as an actress in Isolation Stories, and presented Pooch Perfect.
Read more: Naomi Osaka Netflix documentary to be released in July 2021
What causes conjoined twins?
Conjoined twins are born physically connected to each other.
Identical twins occur when a single fertilised egg (embryo) splits and develops into two individuals.
Conjoined twins develop when an early embryo partially separates to form two.
Although two foetuses will develop, they will remain physically connected.
There’s no known way to prevent it from happening.
Conjoined twins: How long can they survive?
Conjoined twins are always identical because they develop from one fertilised egg.
They are extremely rare and commonly connected at the chest, abdomen or pelvis.
About 70 per cent of conjoined twins are female, although most are stillborn.
After birth, living beyond 24 hours is extremely uncommon.
Who are the oldest conjoined twins in the world?
American twins Ronnie and Donnie Gaylon survived to become the oldest conjoined twins ever recorded.
Sadly, they died from congestive heart failure on July 4 2020.
They were 68 years old.
Doctors felt separating them would be too high risk.
The brothers lived longer than their heroes Chang and Eng Bunker, who lived to be 62.
Lori and George Schappell are currently 59.
How many conjoined twins are alive today?
There are possibly fewer than 12 adult pairs of conjoined twins across the world today.
Famously, Abby and Brittany Hensel from Minnesota are among them.
The teachers share a single body, but have separate heads, hearts, stomachs, spines, pairs of lungs, and spinal cords.
In December 2020, newly-born conjoined twins Yaseen and Yousef underwent a complicated operation to separate them in Yemen.
An echocardiogram showed that each of the two children had their own heart, though the position of the heart of one of them was not normal.
Can both siblings survive?
Both siblings can survive, but it is an extremely rare phenomenon.
Approximately half of conjoined twins are stillborn, and an additional one-third die within 24 hours.
Because conjoined twins often share organs, cases of separation are extremely risky and life-threatening.
Surgeons separated Maltese twins Rose and Grace Attard in November 2000.
The surgery almost certainly meant death for Rose, the weaker twin.
Her heart and lungs were dependent upon Grace’s.
However, if the operation had not taken place, it was certain that both twins would die.
Grace survived to enjoy a normal childhood.
Meanwhile, Great Ormond Street surgeons faced the difficult task of operating on Safa and Marwa Ullah in 2019.
They were joined at the top of the head.
Both girls remained healthy after 52 hours of surgery and the family returned to their home in Pakistan in 2020.
Why are conjoined twins sometimes called Siamese twins?
Chang and Eng Bunker were born in Siam in 1811.
Miraculously, they survived until 1874, and travelled widely for many years.
They were known as The Siamese Twins, and the term is still sometimes used to describe conjoined twins.
Chang and Eng were joined at the torso by a band of flesh, cartilage, and their fused livers.
In fact, surgeons could have been easily separated them had they been alive today.
Extraordinary Twins airs on Wednesday June 20 2021 at 9pm on ITV1.
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