I got pregnant, and sadly miscarried, a few months before DH and i married. We had told everyone we were pregnant, so after the miscarriage SIL and MIL were all waiting with bated breath for an announcment.
However we just got on with it, and this time waited till after the 12 week scan before telling them anything about it. I found out later they were even dreaming about me being pregnant and discussing it constantly.
Straight after DS was born: "when are you having the next one, you need to get on with it if you want three - hahahaha".
Firstly I don't want three, and secondly I am not even sure yet about if and when we will try for a second!
I have handled this by saying - "not ready for a second yet" but not even hinted that we might not have another, as I don't want them involved in those discussions.
They have mostly backed off - but I do know if I even hinted that I wasn't drinking they would be talking about it between themselves, and I suspect they are looking for any suggestions that I might be. However as long as they don't pester me about it I don't really care.
I would second those that say - just tell them you aren't planning on it for the moment, hopefully they then stop talking to you about it, what they talk about among themselves, you have no control over.
Incedentally my mother seems desperate for me NOT to have a second, not quite sure why!