Most mums-to-be have about eight months, give or take a few weeks, to get used to the idea of having a baby once they find out they are pregnant.
Katherine Kropas, on the other hand, barely had enough time to call her parents and tell them the good news before giving birth.
The US woman went to hospital on Tuesday morning complaining of stomach pains.
"I felt like I was getting stabbed in my lower back," Katherine told USA Today. "I have a high tolerance for pain, but this was like a 9" on a scale of 10.
Initial tests showed the 23-year-old was five weeks pregnant, which was not a complete surprise to Katherine.
"I noticed my ankles were swollen and there was a bit of blood. I had no idea I was full-term, though," she said.
However further examinations by nurses revealed Katherine's baby was ready to be delivered.
"My boyfriend Dan asked if he should call my mum," Katherine told USA Today. "'Yeah, you should probably call,' I said."
The shocked grandparents-to-be made it to the hospital one hour later, just in time for the arrival of baby Ellen Olivia Keefe via emergency c-section.
Katherine's father Richard Kropas told Boston news outlet WCVB5 both his daughter and his surprise grandchild were doing well.
"She's perfectly healthy," he said. "I've never seen a more healthy baby."
Katherine and partner of two years Dan Keefe had spoken about the possibility of having children in the future, but had no idea they would become parents so soon.
Katherine did not have any morning sickness during the pregnancy. She recently noticed her ankles had become swollen, but she put that down the fact she had been on her feet 50 hours a week over the holiday period at the catering company she works for.
But despite the shock of becoming a new mum, Katherine is feeling well.
"It's great, I'm very upbeat," Katherine told the New York Daily News. "Everyone has been very supportive."
The fact the pregnancy went unnoticed by Katherine is even more amazing when you consider the size of her surprise daughter.
The baby, who will be known as Ellie, weighed in at an impressive 4.59kgs (10 pounds 2 ounces).
"(People) just say 'you were carrying around 10 extra pounds and didn't know it?'" Katherine told the Daily News. "I don't know why I didn't know. I mean, I'm just excited and I appreciate everyone who is helping."
Katherine is taking unexpected new motherhood in her stride. She will plan a belated baby shower at some stage, but is no rush to hear wedding bells just yet.
First the focus for Katherine and Dan will be on new parenthood.
"We're definitely happy," Katherine told USA Today. "No need to rush anything else at this point."