A doctor points to an x-ray film of female conjoined twins during a medical consultation at a hospital in Chongqing municipality, July 27, 2010. REUTERS/Stringer

Nigerian conjoined twin girls were successfully separated after an 18-hour operation at a Tennessee hospital months after their parents brought them from Africa to the U.S. for the procedure.

Miracle and Testimony Ayeni were separated at Le Bonheur Children's Hospital in Memphis, Tennessee, after the lengthy operation that began on Nov. 7 and ended Nov. 8, the Associated Press reported Wednesday.

The hospital announced the success of the landmark procedure Wednesday morning. The twins, who celebrated their first birthday Wednesday, had been born with their pelvises joined, a rare condition that Dr. Max Langham, who led the surgical team, said only occurs in one of about every 5 million births.

"Without separation, their future wasn't very good," Langham said at a news conference Tuesday. "They would grow up incontinent, unable to walk, totally dependent for all of their care and unable to participate in the world fully."

A Le Bonheur Children's Hospital spokeswoman told the Associated Press that both girls were both “doing very well.” Though the twins face additional surgeries and subsequent rehabilitation efforts, doctors are hopeful about their long-term health.

The girls had been in the Tennessee hospital since they arrived in the U.S. June 28 with their parents Samuel Olusegun Ayeni and Mary Abiodun Ayeni, their older sister and their pastor after being offered free flights from a Nigerian airline. It was their only hope at separating their baby girls after failing to find a hospital nearby that could perform the operation.

Miracle and Testimony were born at a hospital close to their parents’ home in Enugu, Nigeria, which is an eight-hour drive east from the coastal capitol city Lagos. After local doctors failed to combat the rare condition, the twins were flown to several specialist hospitals around the country before being admitted to Lagos State University Teaching Hospital where they remained until June.

Following months of research, the Ayeni parents were referred to Le Bonheur in Tennessee, where hospital surgeons said they would conduct the life-saving operation free of charge.

The most common complication for women bearing twins include preterm labor and birth (born before 37 weeks,) anemia and miscarriage, according to a University of Rochester Medical Center report.

This is the second time that a set of conjoined twins was separated at Le Bonheur hospital, according to its website. Twin boys who had been born joined at the back and pelvis were separated in 2011 after a 13-hour surgery featuring a 35-member team and four surgical specialties: general surgery, neurosurgery, orthopedic surgery and plastic surgery.