Brazilian twins joined at the abdomen and hip were successfully separated Wednesday after a 14-hour operation, but the chief doctor warned post-surgery issues kept the baby girls' lives at risk.

"Regarding the surgery, it went perfectly. No incidents. We managed to separate them keeping them alive," surgeon Zacharias Calil told reporters at the Mother and Child Hospital of Goiania, in central Goias state.

But the 16-month-old girls remained in danger while their organs react to the surgery, which took a team of 40 people to complete.

The chance of both twins surviving a separation operation of their type is 50-50, doctors said.

Marie Luiza and Marie Luana were connected at the abdomen and hip, had three legs between them, and shared the same liver, intestines, bladder, anus and vagina.

Calil said the most difficult aspect of the operation was separating the pelvis and the kidneys, adding: "Luiza's uretric channel was inside Luana's bladder," and vice-versa.

He said the worst complications arose in Luana since she has been left with only one kidney and might require dialysis treatment later Wednesday.

Both girls were in the intensive care unit and their recovery will chiefly "depend on their kidney functions," the surgeon added.

He said difficulties might also arise in one of Luiza's lungs, since it was sharing her chest space with Luana's liver, which surprisingly turned out to have two distinct structures and was easy to separate.

The twins' third leg, which extended downward like a spinal column, was removed and its muscle and bone used to reconstruct other parts of the body, Calil added.

The girl's condition was the second-rarest sibling fusion after conjoined heads. It was detected five months into the pregnancy.