The marathon surgery that began Tuesday was the seventh operation for the 10-month-old girls, and the most complex yet — with doctors working to separate them at the thorax, stomach and pelvis. This time, Chileans were watching on television and the Internet.
On Tuesday morning, Navarrete and her husband, Roberto Paredes, hugged in the doorway of the surgery ward, after kissing their twin babies Maria Paz and Maria Jose.
"A miracle from God is what I'm waiting for."
The twins had lost a lot of blood by Tuesday night, but Navarrete and Paredes had issued a call early in the day for the public to donate blood and doctors said later that they had enough to ease the bleeding problem.
By midnight (0300 GMT), the twins were two-thirds separated.
"We had to completely separate the chest, and now we are starting the final separation stage of the abdomen and pelvic region," Francisco Ossandon, head of the surgical team, told reporters.
"So far, things have gone according to form. We have had difficult times, particularly bleeding, but they have been dealt with successfully," he said.
The operation was expected to last until 4 a.m. (0700 GMT) Wednesday, for a total of 20 hours.
"They have come out of adverse situations before, and if they have come out from that, how are they going to fall behind now?" Paredes asked.
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 Chilean twins presented a particularly difficult challenge to doctors because they were born sharing many of the same internal organs and even urinary system.
Hospital director Osvaldo Artaza said the risks of their operation couldn't be minimized.
"It's a reality and it's necessary to be super-transparent in warning that one or two girls could die," Artaza said. "But the team ... has committed itself with conviction to try to save the two."
He was more upbeat around midnight. "The vitality and resilience of the girls has given us momentum and given us strength to continue with what lies ahead," he told reporters.
Before the procedure started, Ossandon described the twins' case as the "most complex that has been born in Chile."
"Never have we faced such a high risk," Ossandon said. "We don't have another option from the perspective of the quality of life and the expectations for life of Maria Jose and Maria Paz."
Earlier this year, doctors separated the twins' legs, urinary tracts, pulmonary systems and other parts of their bodies.
Navarrete said it wasn't any easier to wait through the latest operation.
If the twins live through the separating procedure, each of them would then have to be sewed shut. About 100 people participated in the procedure, including 25 surgeons and anesthesiologists.
The twins were born in the Villarrica hospital about 470 miles (760 kilometers) from Santiago and were kept under constant medical care, surviving with the aid of an artificial respirator.
