1) Give your parents gifts that say "grandma" and "grandpa" on them. Coffee mugs, t-shirts, or even a calendar with a special announcement of your due date are all great ways to announce your pregnancy!
2) If you do Christmas stockings in your family, get a special stocking for your new baby, and hang that up too. You can put a little card announcing your pregnancy in your new baby's stocking.
3) Who doesn't love to get a family scrapbook for Christmas? If you are crafty, preparing a scrapbook with beautiful family pictures... and a picture of your ultrasound (or positive pregnancy test) on the last page, is a fun and unusual way to let everyone know someone new will join your family.
4) If you are brave and don't have family members who are easily grossed out, consider putting something that indicates a new baby into the Christmas meal. Putting a pacifier in the soup, adding a baby bib into a cake, or putting a plasticized message that says "we're having a baby!" in the bottom of a dish can cause a shock for everyone!
5) You can also wrap your belly with a gift bow, and appear at your Christmas dinner like that! Your relatives might need a while to figure this one out, but it can be a lot of fun.
6) Finally, this one is strictly for sisters (because, we think your dad would be grossed out). Wrap your positive pregnancy test up as a gift, and present that.