The sisters, Lydia and Maya, survived the five-hour surgery in Bern, Switzerland.
Doctors in Switzerland have successfully separated eight-day-old twin girls who were joined at the liver and chest.
The sisters, Lydia and Maya, are believed to be the youngest ever to survive the surgery.
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The girls, who were born two months prematurely in December with their triplet sister Kamilla, were separated during a five-hour operation at a hospital in Bern, Switzerland on December 10.
Doctors had initially planned to separate the girls after a few months but a week after their birth, their conditions began to deteriorate, the Swiss paper Le Matin Dimanche reported.
One of the twins, who weighed just 2.4 pounds each, had blood pressure that was too high, while the other's blood pressure was too low - so doctors were forced to act.
The surgery was unlike anything the surgeons had done before, Barbara Wildhaber, head of pediatric surgery at the Geneva University Hospital, told Le Matin Dimanche.
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"We were prepared for the death of both babies, it was so extreme," she said.
But it was a success.
"It was magnificent," Wildhaber said. "I will remember it my entire career."
The sisters, who are among about 200 separated conjoined twins in the world, are recovering well, the paper reported.
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