smashley I know lots of people have given some fantastic advice but I thought I'd give from my perspective. My baby was 19 weeks but he was a baby, my son, and I consider him to have been stillborn.
We had a memorial service (we don't know what happened to his body) for him and only invited our parents and siblings. I was very clear about who was invited and asked family to disseminate this so we didn't have to deal with it too much. We also asked whoever we told to tell other people so we wouldn't have questions.
On pregnant women, it's only now that I'm pregnant that I don't hate/avoid/get shaky on seeing pregnant women. I had to attend my nans funeral with my pregnant aunt (who was due at my same due date) and that was horrible. However, it would have been better if she'd not ignored me and completely avoided the topic of my baby.
One thing also be aware of is that you won't necessarily get it right and that's not your fault. I lashed out at everyone who was trying to help and was so angry. And actually the best advice I was given is that it doesn't ever get better. I felt that person was telling the truth.
So what I'm saying is, check with their relatives whether you can attend - don't attend unless you know for certain (it's their day), but really really acknowledge the baby. Use her name. Send a card (all our cards are in his memory box) and some flowers whatever happens. Whatever you do don't sign 'from bump'. Don't talk about your baby. Maybe later on if the atmosphere is right ask about the baby, how much did she weigh, what did she look like, etc. The sadness is overwhelming but the joy is still there and most people don't realise that we've want to keep their memory alive.