En cloque is a slang expression that means “pregnant”. It is not that common, but you may still hear it. It is also the title of a song by Renaud. The usual word, enceinte, can be used in colloquial conversations.
Note that this expression is not extremely elegant: une cloque means “blister”.
You can say mettre enceinte or mettre en cloque to say “impregnate”. The slang word engrosser is the equivalent of “to knock up”. It’s not elegant either: I’d avoid using this verb in front of the concerned people. This word actually comes from grosse, an older word for “pregnant” (but nowadays you shouldn’t use it to talk about a woman, you’d just call her fat).
I like the expression (colloquial but not very common) avoir un polichinelle dans le tiroir, literally “to have a Pulcinella in the drawer”, which is the equivalent of “to have a bun in the oven”.