In this case, it's better not to ask

Ok people I'm getting on my soap box....I understand that the natural progression after getting married is to have kids. And, when 2 1/2 years pass it is only natural to wonder if kids are in the plan. But please stop and think before asking "when are you gonna have kids?" or "are you pregnant yet?" It's possible that the person on the receiving end of those questions gets emotional after explaining over and over again. Just because they aren't having children doesn't mean they don't want them and pain they feel by the fact that they are having a hard time cannot be understood unless you've been there. Pray instead...that's probably what they are doing.
Off my soap box now :)