Christina Marie Birch (born November 17, 1986) is an American professional racing cyclist and NASA astronaut.

Birch grew up in Gilbert, Arizona, and graduated from the University of Arizona with a bachelor's degree in mathematics, biochemistry, and molecular biophysics. Birch began cycling with the MIT cycling team while working on her PhD. While at MIT she won the 2014 USA Cycling collegiate cyclocross division two national championship. Birch also represented the JAM Fund cyclocross team from 2011-2015.^[1]

After earning a doctorate in biological engineering from MIT in 2015, Birch moved to Southern California to pursue track cycling full time. She taught bioengineering at the University of California, Riverside, and scientific writing and communication at the California Institute of Technology. On the track, Birch has represented the US at multiple Pan American Championships, World Cups, and World Championships. She competed at the 2018 and 2019 UCI Track Cycling World Championships, and the 2019 Pan American Games.^[2]

Birch was named to the US track cycling 2020 Olympics long team for the USA in June 2020.^[3]

On December 6, 2021, Birch was formally announced as a NASA astronaut candidate with NASA Astronaut Group 23.^[4]

She is a partner of a racing cyclist Ashton Lambie.^[6]