1 of 2
Luis Calvo Mackenna Hospital, Associated Press
In this image taken from a video released by Luis Calvo Mackenna hospital, conjoined twins Maria Paz and Maria Jose Paredes Navarrete are seen prior to a surgery to separate them in Santiago, Chile, Tuesday, Dec. 13, 2011. Chilean doctors started a long and dangerous surgery to separate 10-months-old conjoined twins who are joined at the chest, stomach and pelvis.

SANTIAGO, Chile — Chilean doctors successfully separated conjoined twin girls in a marathon 20-hour surgery, saying Wednesday that the operation went extremely well despite challenges.

The 10-month-old twins Maria Paz and Maria Jose were recovering in an intensive care unit, and doctors said the next two days would be critical as they watch for infections or other possible complications.

Parents Jessica Navarrete and Roberto Paredes kept an anxious vigil at Luis Calvo Mackenna Hospital in Santiago as doctors separated the twins at the thorax, stomach and pelvis. It was the seventh and most complex operation yet for the twins.

Doctors said the twins were successfully separated late Tuesday night. Chief surgeon Francisco Ossandon described it as the moment "the girls finished the process of being born."

"Before, they had two souls and one body," Ossandon said.

Surgery on one of the twins was completed early Wednesday after a total of 19 hours, while for the other it took more than 20 hours.

"We had a number of difficulties during the surgery. There were some surprises, but we were able to fix, solve the problems," Ossandon said at a news conference.

He added that the twins came out of the surgery in good condition. Ossandon, however, didn't rule out future complications involving the effects from anesthesia and possible infections.

"We're very happy because we think they've had the best evolution we could have hoped for," he said.

The girls' parents appeared in televised images as they kissed the twins before the operation. Then afterward, the mother and father gazed lovingly at the sleeping girls from beside their separate cribs in the intensive care unit.

Some Chilean television stations occasionally broke into their regular programming to broadcast updates from the doctors, both during and after the delicate surgery.

Navarrete said she was waiting for a miracle from God when the high-risk operation began Tuesday morning.

The Chilean twins presented a particularly difficult challenge because they were born sharing many of the same internal organs and even urinary system. About 100 people participated in the procedure, including 25 surgeons and anesthesiologists.

Perhaps providing some comfort to the parents was the hospital's history with conjoined twins. Staff there have separated three sets before. A fourth set, however, died during surgery due to cardiac complications.

According to the University of Maryland Medical Center, one out of every 200,000 live births worldwide results in conjoined twins. About 35 percent survive only one day, while the overall survival rate is 5 percent to 25 percent.

The twins were born in the Villarrica hospital about 470 miles (760 kilometers) south of Santiago and were kept under constant medical care, surviving with the aid of an artificial respirator.

Earlier this year, doctors separated the twins' legs, urinary tracts, pulmonary systems and other parts of their bodies.

During the latest surgery, doctors managed to separate an intestine that had been shared by the two, giving each of them part of it, said Jaime Manalich, the government's health minister, who visited the family at the hospital.

Surgeons weren't able to completely close their abdominal cavities or their thoraxes, and therefore had to use meshing to cover them, Ossandon said. "These are foreign bodies that sometimes the body recognizes as foreign, and that can cause infections," he said.

Maria Jose was the first twin to reach the intensive care unit after the surgery. Her sister Maria Paz, whose operation was more complex due to difficulties in the area near her heart, arrived an hour and 15 minutes later.

They were born in February, and since then have been hospitalized and attached to machines including an artificial respirator.

The girls were still connected to a respirator on Wednesday, and are to remain sedated for at least 72 hours.

Ossandon said the twins will return to the operating room every two or three days so that doctors can clean their wounds. He called the surgery their "rebirth."