A 35-year-old Canadian woman has given birth to rare identical quadruplets, hospital officials said Thursday.

Karen Jepp of Calgary, Alberta, delivered Autumn, Brooke, Calissa and Dahlia by Caesarian section Sunday afternoon at Benefis Healthcare Hospital in Great Falls, Montana, said Amy Astin, the hospital's director of community and government relations.

The four girls were breathing without ventilators and listed in good condition Thursday, Astin said.

"These babies are doing grand," said Dr. Tom Key, the perinatologist who delivered the girls.

The babies were born about two months early and were conceived without fertility drugs, he said. They weighed between 2.6 pounds (1.18 kilograms) and 2.15 pounds (0.98 kilograms).

Jepp and her husband, J.P., declined to be interviewed by The Associated Press.

The couple also have a 2-year-old son, Simon.

J.P. Jepp works for Shell Oil Co., and both parents worked for nonprofit groups until recently, Astin said.

The chances of giving birth to identical quadruplets is about one in 13 million, Key said.

"This is a very big medical event," he said. "Identical quadruplets are extremely rare."

Medical literature indicates there are less than 50 sets of identical quadruplets, said Dr. Jamie Grifo, director of the NYU Fertility Center in New York.

The last reported set were born in April 2006 to a 26-year-old Indian woman.

The Jepps drove 325 miles (523 kilometers) to Great Falls for the births because hospitals in Calgary were at capacity, Key said.

Two of the girls were to be transferred to a Calgary hospital later Thursday. The other two could be moved Friday if their conditions remain favorable, Key said.

They will likely remain hospitalized for four to six weeks, he said.