How to tell grandparents

Callie
I'm going to start off by saying I'm 23 and will be 24 by the time baby is here, unmarried but in a stable relationship, and have pretty much been on my own since after high school when I was 18. My little sister ended up a "teen mom", giving birth at 18. She kept the baby and now has a happy, healthy, loved nearly 2 year old. Where my dilemma comes in is telling my grandparents. They are in their 80s, very religious, and pretty judgmental. They tried for months while my sister was pregnant to convince her to give up her baby and I know it was very stressful for her. When I told my parents at 8 weeks they agreed to not yet tell my grandparents as it would most likely just add stress to me. I'm 19 weeks tomorrow. My grandparents still don't know. How should I go about telling them? I will be seeing them November 12, if not sooner, for my sister's wedding. So I feel like it would be pretty cruel to just show up obviously pregnant and not have them know. Sorry for the long post.