Well, I just heard a third pregnancy announcement in as many weeks, and that triggered the tears. I didn't cry at all with the first two. I blame, at least a little, PMS, and the fact that my husband slipped the other night and said "our kid is going to have" and then quickly changed to "our kid would have had...." Just thinking about it makes me sad because it tells me he's not quite as moved on as he likes to say he is. I think he's probably in about the same place as me: accepting of our new life, but certain reminders (of what we would have done with our kids, that other people get to do those things and not us) feel like a kick to the stomach.
Apparently, I can handle two kicks to the stomach. Three set me over the edge.