Although "knocked up" means pregnant in the United States, it has quite a different meaning in Britain, as I found out during a year abroad.
To "knock someone up" is to knock on their door in the morning to wake them up. Nothing more.
When I was staying in Yorkshire at Christmas, we planned a long day out. I didn't have an alarm clock with me, so my friend's mother said she would knock me up in the morning.
I managed to thank her in an even tone of voice, and get out of the room before I started laughing. I could never bring myself to explain to that gentle soul what she had said to me.
As American slang spreads to the UK, the British phrase is falling out of use. A shame, really.