According to doctors, Kendra and Maliyah Herrin shouldn't have lived past 24 hours.
But the conjoined twins beat the odds and were successfully 'cut in half' at age four. They now live life as typical teenagers who have one leg each.
The sisters, who only shared one kidney, an abdomen, pelvis, liver and large intestine - are the focus of a BBC Three documentary, Living Differently, that reveals all about their risky 26-hour operation.
Find out what it's like to be Kendra and Maliyah here:They were born conjoined in Salt Lake City, Utah, and it took years of deliberating for their parents Jake and Erin to agree to the surgical separation.
At the time, surgeons had never separated twins with one kidney and their operation took months of careful planning and research.
The operation came with great risk; doctors told Jake and Erin that if it went well, it would give the girls independence and the chance of a longer life, but if it failed, it could kill them.
Thankfully, in the end, the twin's unprecedented separation surgery - which lasted longer than a day - went smoothly and they were out of hospital within six weeks.
However, they have had to go through life with one leg each, as well as endure spine-straightening and plenty of trips back to the hospital over their lives to deal with their rare medical condition.
After the operation, Kendra was left with their one kidney, meaning Maliyah has had to have a number of kidney transplants.
The young woman was given her first kidney at age five, which came from her mother. This organ lasted ten years but when she was 15 started to fail; Maliyah was forced to go on dialysis before getting a new one from an anonymous donor a year and a half later.
Despite their pioneering medical history, if you ask the girls, they're just your average teenagers.
"When people first hear our story, they like to ask a lot of questions," Kendra said in the BBC Three documentary. "But simply we feel like we're the same as everybody else, we just have a few things that are a little different."
Maliyah added: "Our parents talked to us about 'cut apart day,' but we were so young we didn't really understand what was happening."
Nowadays, the two girls - who also suffer from scoliosis and have rods in their back - attend school, do daily chores for their parents and hang out with their family. They also enjoy a huge following online, with their own blog, Youtube channel and Instagram account.
The pair claim they are grateful their parents decided to go through with the surgery, and appear to be thriving in their unusual circumstances.
"The best thing about only having one leg is we only have to paint on set of toenails," Kendra joked.
