AURORA, Colo. — A Colorado hospital where a Minnesota woman gave birth to conjoined twins said Thursday that one of the babies died after a complicated five-hour separation procedure.

Amber McCullough delivered the twin girls, Hannah and Olivia, by cesarean section on Wednesday. Doctors had to immediately separate them due to the severity of their heart condition, Children’s Hospital Colorado spokeswoman Elizabeth Whitehead said.

Olivia, who was not expected to survive because of problems with her heart, died. Hannah is in critical, but stable condition, Whitehead said. McCullough, a Hastings native, is recovering.

A team of doctors performed the procedure 32 weeks into McCullough’s pregnancy.

The twins shared an abdomen, liver and intestinal tract. The girls had separate hearts and kidneys. McCullough said in Olivia only had a single ventricle in her heart and was missing valves.

“I believe in the power of prayer and the talent of the medical professionals here,” McCullough said in a statement released through the hospital.

Conjoined twins happen once every 200,000 live births, according to the University of Maryland Medical Center, which says between 40 to 60 percent arrive stillborn.

Surgical separation is still rare, according to the medical center, which says that, since 1950, at least one twin has survived separation about 75 percent of the time.

McCullough said she spent eight years in the U.S. Army, then went to law school and is now an attorney. She has a 6-year-old son named Tristan from a previous relationship that ended in divorce. She said her son is moving to Denver to be with her soon.