She gave unexpected birth to a baby girl.

Runners have to prepare themselves for all kinds of surprises during their training, but the surprise experienced by 33-year-old Trish Staine of Duluth, Minn. takes the cake.

According to CBS News, Staine, a half marathoner, experienced severe back pain early this week. It turns out she was pregnant and ready to give birth.

Staine says she had no idea that she was carrying a baby and never experienced a fetal heartbeat and had not gained any weight. On top of that, her husband had underwent a vasectomy.

“I said, ‘No, no, that’s impossible,” said Staine, a mother of three after giving birth. “I definitely thought I was done having kids.”

Staine had been training for the Grandma’s half marathon.

In addition to her three children, Staine has three stepchildren from her husband’s first marriage.

“I had a sore back Sunday evening. I had taken a hot shower and was dealing with it,” Staine recalled. “Monday morning, I woke up and had more back pain, and as the day went on it got worse. I thought I should go to the ER. I thought I ruptured a disc or pulled a muscle.”