Doctors have successfully taken the first step toward separating the fused legs of Milagros Cerron, a 9-month-old Peruvian baby dubbed the “Little Mermaid” because of her rare birth defect, her parents said on Wednesday.

“Everything went well, but it’s a tough time. Her mother is crying, we’re crying,” her father Ricardo Cerron, 24, told Reuters after Tuesday’s operation to begin correcting the condition, which is nearly always fatal.

Milagros, whose name means “miracles” in Spanish, was born with “mermaid syndrome,” or sirenomelia, a condition affecting 1-in-60,000 to 1-in-100,000 people. Only a handful of patients have survived more than a few hours and there are few precedents for the risky separation surgery.

Milagros, who weighs 17 lbs (7.5 kg) and is 24 inches (60 cm) long, has a healthy heart and one good kidney but the other is tiny, said Luis Rubio, the doctor leading the team which plans to cut her legs apart next month.

Although Milagros’ legs are joined seamlessly from her abdomen to her heels - with her tiny feet splayed in a “V” completing the resemblance to a mermaid’s tail - her legs have separate bones, cartilage and blood supplies, and can be seen to move independently inside their “sack” of fat and tissue.

She has a rudimentary anus, urethra and genitalia, all located together, Rubio said. Genital reconstruction will probably wait until adolescence, he said.

The four-hour operation to insert silicone bags between Milagros’ legs to stretch the skin “was a success,” said hospital spokesman Inti Lozada.

Little incisions were made between Milagros’ ankles, knees and thighs and silicone bags slipped inside.

Doctors will gradually add saline solution to the silicone bags to pump them up like balloons - a technique widely used in plastic surgery - to stretch the skin enough to cover the exposed wounds once her legs are separated next month.

“I’m worried. I’m sad. I’m tired,” said Milagros’ mother, 19-year-old Sara Arauco.

“She woke up crying (in the night)...I’m worried about the pain she will feel…about her feeling uncomfortable,” Arauco added.

Mermaid syndrome is about as rare as conjoined twins but it is nearly always fatal since most sufferers lack kidneys or have other complications.

Sixteen-year-old Tiffany Yorks of New Port Richey, Florida, whose legs were successfully separated when she was a baby, says she believes she is the world’s only survivor.

TWO DECADES OF OPERATIONS AWAIT

Milagros, who was born on April 27, 2004 in the eastern Andean town of Huancayo, has been cared for since she was two days old at a City Hall-funded hospital run out of old buses in a poor north Lima suburb.

Dark-haired and pretty, she babbles and smiles like any other baby, is learning to sit up and looks totally normal from the waist up. But she faces a grueling series of operations that Rubio, her doctor, hopes will enable her to live an independent life.

“We know we’ll be treating (Milagros) for the next 18 years,” he said.

In mid-March, at least 10 specialists working “centimeter by centimeter” will cut her legs apart as far as her lower thigh. Another operation expected three months later will divide them as far as her pelvis.

“We hold a great deal of hope for this child,” said Geoffrey Blair, a doctor at the British Columbia Children’s Hospital in Vancouver, who helped treat another mermaid case. He declined to comment on whether that patient survived.