A medical team in Switzerland successfully separated what is believed to be the youngest pair of conjoined twins ever, officials at Bern University Hospital said Sunday. The girls were born premature and joined extensively at their liver.

Pediatric surgeons from the Bern Pediatric Clinics along with colleagues from the Geneva University Hospitals announced the successful separation. The twins, who had a number of large blood vessels shared between them, endured a five-hour operation on Dec. 10. The girls were 8 days old.

"Such small conjoined siblings have never been successfully separated before," the hospital said in a news release.

The girls, born eight weeks before their due date, were "extensively conjoined on the liver, but had all vital organs," the hospital said.

"It is the first successful operation of such small conjoined twins in Switzerland and possibly even worldwide, and therefore -- apart from great luck for the parents -- a medical sensation."

The twins were among a set of three children born Dec. 2, according to the hospital. They were born in the 32nd week of pregnancy by Cesarean section. Their sister was born healthy.

Together, the conjoined twins weighed 2,200 grams (4 pounds 14 ounces).

"They had great problems, because a very great amount of blood flowed from one child to another through the liver," the hospital said. "That is why one child had too much blood and blood pressure that was much too high while the other child did not receive enough blood and had blood pressure that was too low."

Doctors were able to separate the pair, who are now recovering in the hospital's pediatric intensive care unit. Officials said the two "still very small children are developing quite well."

"The perfect teamwork of physicians and nursing personal from various disciplines were the key to success here," said Steffen Berger, head of Bern university Hospital's Department of Pediatric Surgery. "We are very happy that the children and parents are faring so well now."