Runner Trish Staine went into labor unbeknownst to her and checked into a hospital for simply severe pain on Monday.
The aspiring half-marathon runner had mistaken her aching back and other pains as the result of a two-hour run.
However, 33-year-old Staine delivered a baby girl just minutes later.
Staine had been admitted to the Essentia Health-St. Mary's Medical Center in Duluth, Minn, according to the Associated Press.
The runner and her husband, John, were completely unaware of the pregnancy due to John's vasectomy.
"I said, 'No, no that's impossible," Staine explained to WDIO-TV of nurses finding a fetal heartbeat on Monday.
In addition to her husband's vasectomy, the mother of three recalled that she had not gained any weight or felt any fetal movement in the months before.
"I definitely thought I was done having kids," she added. Staine and her husband have a 7-year-old daughter and an 11-year-old son, and the runner is stepmother to John's three sons aged 17, 19, and 20.
Staine recounted the mysterious pain following her run, stating: "I felt like I was dying, I didn't know what was going on."
Once she had arrived at the hospital, Staine was shocked to discover her pregnancy as well as the arrival of her baby girl Mira- short for Miracle.
The baby arrived about five weeks early on Monday, weighing 6 pounds and 6 ounces and was 18.9 inches long.
The runner said her husband maintained a good sense of humor.
"He's still in shock," she said to the local news station. "Everybody is teasing him."
Undetected pregnancies that are only realized until delivery happen in about one in every 2,500 births, according to ABC News.
The Discovery television series "I Didn't Know I Was Pregnant" reveals the stories of women who were unaware of their pregnancy until the child's arrival.