Doctors upgraded the condition of separated conjoined 4-year-old twins Sunday to serious but stable.

Kendra and Maliyah Herrin, who were born fused at the mid-torso, had been in critical condition since their separation in a 26-hour surgery that ended Aug. 8 at Primary Children's Medical Center. They were removed from ventilators Saturday.

Doctors waited to upgrade the twins' condition until the girls spent 24 hours breathing on their own, hospital spokeswoman Laura Winder said.

"They've made it 24 hours now, so the odds that they'd need to go back on ventilators is less," she said.

The girls remain on heavy pain medication in the pediatric intensive care unit. Winder said they have opened their eyes, but it's unclear how aware they are.

Before the surgery, the North Salt Lake girls shared a liver, kidney, bladders, a single pelvis and two legs, one controlled by each girl.

A team of six surgeons separated their bodies, liver and bladder, and reconstructed their divided pelvis. Each girl kept one leg and Kendra kept the kidney, which was in her body.

Maliyah is on dialysis and is expected to get a kidney donated by her mother.