Amber Miller finished the Chicago Marathon three hours off her pace on Sunday, clocking in at six hours and 25 minutes.

But there's a good explanation for why.

Miller was almost 39 weeks pregnant, ran through contractions, and delivered a daughter shortly after the race ended.

“The race was definitely easier than labor,” Miller, 27, said on Monday.

Miller's doctor signed off on Miller's plan to run, and Miller had already finished the Wisconsin Marathon earlier this year while pregnant. She said she wasn't sure if she was in labor during the race because she commonly feels contractions while running.

Running with a bun in the oven certainly didn't scare Miller, who's now finished eight marathons. She said, "I know what I can handle. This is something I’ve been doing for a long time."

The mother and baby are both reportedly healthy and resting.

More From TSM Interactive