A few hours after completing the race Sunday, the suburban Chicago woman gave birth to her daughter, June.
The 27-year-old is an experienced marathoner who found out she was pregnant after signing up for the race months ago. She figured she'd play it by ear on whether or not she'd run.
Miller was nearly 39 weeks pregnant by Sunday. She got clearance from her doctor to half run and half walk the race.
She finished in six hours 25 minutes, much slower than her previous seven marathons.
Miller spoke to The Associated Press from the hospital and says she received encouraging cheers during the race and never felt bad, except for some feet blisters.