Doctors successfully separated 4-year-old twin sisters born fused at the midsection, with just one kidney and one set of legs, and were continuing with reconstruction surgery early Tuesday.

Kendra and Maliyah Herrin were separated after nearly 16 hours of surgery at 10:50 p.m. Monday, which was about an hour earlier than had been expected. Ten minutes later, Kendra was moved to a separate operating room and the single surgery became two separate procedures.

"It's exciting they're doing really, really well," said Rebecka Meyers, chief pediatric surgeon at Primary Children's Medical Center. "When a patient does well, it's awesome. It's what you hope for."

The final stages of the surgeries -- expected to finish at a different time for each girl -- included the reconstruction of their pelvic rings and several internal organs.

Earlier in the surgery, doctors divided the girls' shared liver and severed Maliyah's connection to Kendra's kidney.

Maliyah will be placed on dialysis and is to get a kidney from her mother, Erin Herrin, within three to six months.

Meyers said it was the first known surgical attempt to separate twins with a shared kidney.

When the blue-eyed, sandy-haired girls wake up, it will be the first time they won't be locked in an embrace.

The twins are expected to remain in intensive care for about a week and recover in the hospital for at least a month before doctors can consider sending them home, Meyers said.

Conjoined twins occur about once in every 50,000 to 100,000 births. Only about 20 percent survive to become viable candidates for separation.

In most instances, conjoined twins undergo separation surgery between ages 6 and 12 months, but the Herrin's shared kidney forced a delay.

Erin Herrin, 25, broke into tears and fell into the arms of her 26-year-old husband, Jake Herrin, when the couple was told the surgery had been successful. Relatives applauded.

The North Salt Lake couple said they were nervous about seeing the girls separate for the first time.

"I don't know that it's set in yet," Jake Herrin said. "We're not going to feel totally comfortable until they're out of the OR and everything's stable."

"And we can hold them," his wife added.

The couple, who also have a 6-year-old daughter and twin 14-month-old boys, said they were anxious to tell the girls how brave they had been and how proud they've made their family.

Jake Herrin even cracked a few surgery jokes.

"Most people say, 'You made it through in one piece," he said. "We can say, "You guys made it through in two."'