My wife wants to try for a baby... Problems with discussion.?

For every other night for the past two weeks, my wife discusses how she wants to try for a baby. When I say that I am not ready yet, she locks herself in the bathroom shrieking and crying until I finally agree to try for a baby. I don't want this to continue because she might get pregnant when I am not ready to have a baby, but I love my wife and I don't want to lose her.