Katie Kropas was rushed to the hospital on Tuesday morning with lower back pain.
Three days later she's preparing to go home with a new baby.
The instant mom was shocked because she says she didn't know she was pregnant.
"I thought I had put on...like some Christmas season weight, you know, but I never thought I was pregnant, never," said Kropas.
Doctors say it's called a "cryptic" pregnancy."
They say it happens more often than you think, especially if the woman is overweight or has irregular periods.
It's even the subject of a show on TLC called "I Didn't Know I Was Pregnant."