An 82-year-old Colombian woman went to the doctor for pelvic pain and found that she was carrying a "stone baby."
The woman was told her pain was from a four-pound calcified fetus, called a lithopedion, that she had been carrying for decades, without realizing it, according to the Telegraph .
The doctors found the rare medical phenomenon after ordering an X-ray that revealed the lithopedion, or "stone baby."
Dr. Kim Garcsi, who directs the ob/gyn clerkship program at University Hospitals Case Medical Center in Cleveland, told ABC News that the condition is so rare, it's only been recorded in history 300 times.
Garcsi told ABC that this occurs when the pregnancy fails, usually because the fetus doesn't have enough blood supply, there is no way for the body to expel the fetus.
As a result, the body turns the fetus to "stone." It's a process our immune system uses to protect us.
"When you get old cartilage in the knee, it calcifies," Garcsi told ABC, trying to explain the way this process works.
The calcification of the tissue protects the mother from infection but also means the baby can stay in the abdomen undetected for decades.
In this case, the fetus is 40 years old.