— -- Katherine Kropas had no idea she was pregnant with a 10-pound baby until an hour before she gave birth.
"They took one look, and they rushed me off into labor," she told ABC's Boston station WCVB. "I found out that I was having a baby at 10:15. She was born at 11:06 p.m."
She gave birth to a baby girl, Ellie, who weighed 10 pounds and 2 ounces. Kropas told WCVB she felt that she'd put on some weight, but figured maybe it was just typical holiday weight gain.
Ellie's grandmother, Karen Kropas, told WCVB she's heard of this happening, but never thought she would see it firsthand.
"You laugh and you say that's ridiculous," she told the station. "And then it happens to you, and you're like, 'This really does happen.'"
South Shore Hospital in Massachusetts told WCVB that it happens about once or twice a year there. In a Berlin study of 29,462 births published in the British Medical Journal in 2002, researchers determined that a one in 475 women did not realize they were pregnant until about 20 weeks gestation and one in 2,455 didn't realize it until they went into labor.
Dr. Jennifer Ashton, a senior medical contributor for ABC News and practicing OB/GYN, said she's seen cases like Kropas's in her career.
"It tends to happen in women who are overweight or obese to start, may have irregular periods and are less aware of their bodies," Ashton said. "For most women who have been pregnant, they are aware of multiple physical signs and symptoms, and those signs and symptoms are not subtle."
She said though this case is incredible, it's far from desirable.
"It represents a missed opportunity for prenatal care for the baby, which is definitely not ideal," she said.