A teacher who lost her job at a Catholic school in Kansas City, Missouri, after becoming pregnant has testified that she believed administrators decided not to renew her contract because she wasn't married but created a paper trail of evidence to justify their decision.

The Kansas City Star reports that Michelle Bolen testified on Monday in her lawsuit against the former principal of St Therese Catholic elementary school and the Diocese of Kansas City-St Joseph.

Ms Bolen had worked for the school for nearly 15 years when she lost her job in July 2015.

She now works at another school. Her attorney said the former principal had never failed to renew a teacher's contract after having overseen 330 performance reviews over nearly a decade.

A lawyer representing the diocese has said the case wasn't about her pregnancy, and that Ms Bolen was intent on getting "revenge".