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Associated Press
In this image taken from a video released by Luis Calvo Mackenna hospital, Roberto Paredes, right, caresses his daughter Maria Jose, one of two conjoined twins after she was separated from her sister Maria Paz at the Luis Calvo Mackenna hospital in Santiago, Chile, Wednesday, Dec. 14, 2011. The 10-months-old twins were 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, abdomen and pelvis. It was the seventh and most complex operation yet for the twins.

Doctors successfully separated the twins 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.

Paredes softly placed a hand on one daughter's head.

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

"The next 48 hours will be the most critical in terms of the ... risk they face of dying," said Dr. Carlos Acuna, chief of the intensive care unit. He said the girls faced risks of various organs ceasing to function, and also had kidney and lung problems.

The girls' mother said she was hoping for a miracle 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, roughly one out of every 200,000 live births worldwide results in conjoined twins. The overall survival rate is between 5 percent to 25 percent, depending on various factors, including where they are joined.

While rare, such surgeries have become increasingly frequent over the years due to improvements in surgery, anesthesia and critical care, said Dr. Eric Strauch, a surgeon at the University of Maryland Medical Center.