Salt Lake City ? Four-year-old twin sisters born fused at the midsection, with just one kidney and one set of legs, underwent surgery Monday to separate them and allow them to lead independent lives.

Doctors at Primary Children’s Hospital said it was the first known surgical attempt to separate twins with a shared kidney.

Kendra and Maliyah Herrin were rolled into the operating room at 7:15 a.m. after a tearful goodbye from their parents.

“It was very emotional,” said their father, Jake Herrin. “They were more brave than us.”

The operation was expected to last 12 to 24 hours, during which surgeons planned to give each girl one leg and Kendra the kidney. Maliyah will be put on dialysis for three to six months until she is strong enough for a transplant of a kidney from her mother, Erin Herrin.

Surgeons also planned to divide the girls’ single liver, separate their intestines and reconstruct their shared pelvis.

The twins were stable through the first hours of the operation.