Hi Nicole
Maybe you could just let them know that you understand that your pregnancy might be difficult for them. I think it is better to let people know that you are trying to understand and empathise than to ignore the issue. Of course, you need to be very sensitive and obviously not constantly gushing about baby and how wonderful it is (I know you wouldn't do that anyway). But I also think it would hurt if you excluded them completely from that part of your life by just avoiding the subject.
Do you have the kind of relationship where you could talk to them and say you can't imagine what they are going through but that you want to try and be there for them? Often people need a chance to talk about these things and to have a cry. It can be very sad to talk about babies but they might want to have a chance to do that. Just let their conversation and actions lead yours.

((hugs)) you don't need to feel guilty, just try and empathise and reach out to them however you can.