We didn't tell anyone with either of ours. But we didn't have any trouble conceiving - I guess people who take a long time might need some support. I also found it a bit annoying how people would keep on asking if/when we were having children. My FIL's partner actually asked whether I was pregnant when we announced our engagement!! As we did not have our first child until we had been married nearly 7 years, we had a lot of nosy questions before then. We tended to answer jokingly, yes we're having 10 (or 20) and then change the subject. At this stage we've told everyone that we are "hoping to have another child one day" but we certainly won't be making an announcement the month we start trying.