OKLAHOMA CITY (AP) - A set of 1-month-old girls believed to be the first known American Indian conjoined twins are doing well and will be separated, doctors say.

Preslee Faith and Kylee Hope Wells were born Oct. 25 and are joined at the liver and rib cage, said David Tuggle, a pediatric surgeon who will be involved in the separation.

"They are very cute and they hold each other," Tuggle said Tuesday of the twins.

The twins' parents are 21-year-old Kyle Wells and 20-year-old Stevie Stewart of Calumet. Both have a history of twins in their families.

Stewart, a member of the Cheyenne River Sioux tribe, said the girls already are developing personalities. For example, Kylee "is laid back and sleeps through anything, even her sister crying," Stewart said.

"I can't wait to take them home."

Tuggle said the twins, who weighed a combined 8 pounds, 7 ounces at birth, appear to have separate hearts, but doctors want to learn if the girls share blood vessels around their hearts before performing the separation.

"The thing about conjoined twins is that there is always something you don't know exactly about them," Tuggle said.

Tuggle said conjoined twins are rare and occur in about 1 in 600,000 births in Oklahoma. He said the condition happens soon after conception because of an error in cell division and is random.

Doctors learned of the twins' tissue connection during a routine ultrasound exam done when Stewart was 20 weeks pregnant. The babies were born at 34 weeks via Caesarean section.

Since birth, they have remained in an intensive care unit at the University of Oklahoma Medical Center, where they have been "on and off" breathing machines, said Kris Sekar, a neonatal doctor who has been overseeing their care.

"They have great days and off days, but we have done very well," Sekar said.

Stewart, who wept at times while speaking with reporters, said she is allowed to hold her babies whenever she wants and changes their diapers, but allows nurses to dress the twins.

Stewart's mother, Marla Longbrake, said her daughter has handled the stressful situation well.

"It was a shock, but she and the father didn't question it," Longbrake said of learning of the twins' condition. "They're just happy, beautiful little girls."

Tuggle said he has "no idea" how long the surgery might last or when it might take place, because the twins need to grow bigger and stronger first. He said it would be good for the surgery to occur before the twins are eight to nine months old, to help with their psychological development.

Tuggle participated in the last surgical separation of conjoined twins at OU Medical Center, which occurred in 1986. Those twins, Faith and Hope Cox, are healthy and now in their 20s.

Stewart said she has spoken with Natalie Cox, the mother of the Cox twins.

"It is nice to be able to talk to someone who's been through this," she said. "She said if I ever need anything to call her."