(AP) -- Conjoined twin girls who were separated in a 20-hour operation were in critical condition on Friday and one was in danger of dying, according to the director of the Chilean hospital where they are being treated.
Doctors have been closely watching the 10-month-old twins for any complications since Tuesday's operation and Hospital director Osvaldo Artaza said that Maria Jose suffered "an episode of cardiac complications that required reanimation and extraordinary measures."
"That means that Maria Jose ... has a certain risk of dying," he said.
Surgeon Francisco ossandon performed a follow-up operation on both girls on Friday to change meshing that had been used to cover part of the twins' body cavities after the surgery at the Luis Calvo Mackenna hospital in Santiago, Chile's capital.
Doctors had said from the start that the most dangerous period for complications would arise 48 to 72 hours after the complex operation that ended early Wednesday. It was the seventh that the two girls had undergone since their birth at a hospital in Villarrica, about 470 miles (760 kilometers) south of Santiago.
The twins presented a particularly difficult challenge because they were born sharing many internal organs and even urinary system. About 100 people participated in the separation procedure, including 25 surgeons and anesthesiologists.
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.
Earlier this year, doctors separated the twins' legs, urinary tracts, pulmonary systems and other parts of their bodies. They now each have part of a leg that used to be fused together. During the latest surgery, doctors separated an intestine that had been shared by the two.
Explore further: Chilean doctors separate conjoined twins