In American English, "Knocked up" means "pregnant." I just found out via an article regarding jobs that no longer exist that in British English, they use use the phrase "Knocked up in a completely differnt way. This due to the job of knocker-uppers being the tapping or knocking on windows to awaken people in the days before alarm clocks. From "Knocked up" to mean "woken up", it appears that the meanings split somewhere between the 1920s and the 1940s.
Does anyone know the history of how the meanings split and exactly why and how it happened?