As the others above have said, it can mean pregnant, or to make someone pregnant, at least in American English. In British English to knock someone up means to wake someone up by knocking on the door. http://dictionary.reference.com/browse/knock-someone-up

There has to be more context to be certain but just "knocked up" by itself usually means pregnant. "He knocked her up." means he got her pregnant. "Don't knock her up." means don't get her pregnant. "I'm knocked up." means she's pregnant. "The ball was knocked up in to the bleachers." means that the ball was hit or deflected into the bleachers. There is a movie title called "Knocked Up" and my sister let us borrow the DVD. She was at my house one day and I stood up and my wife asks what I was doing. "I'm getting my sister Knocked Up." and then we laughed because it sounded like I was getting her pregnant but I was simply returning the movie to her.

"knocked up" in one context could mean that you are pregnant and are going to have a baby