Where did the term "knocked up" come from for being pregnant ?

Answer 1

During the mid to late 1800s, "knocked up" referred to injuring or impairing somebody. It's assumed that it morphed into a pregnancy reference due to the limitations that come with carrying a baby in the womb.

Possibly it is also related to knock in the sense of "to copulate with" (1598; cf. slang knocking-shop "brothel," 1860), according to the ONline Etymology Dictionary.