telling your parents you're pregnant

my husband and I are still ttc but I've been thinking a lot lately about how we are going to tell the family when we finally do get pregnant. my parents already have a grand daughter from both of my brothers and my husband's parents don't have any grandchildren. I can think of countless ways to tell his parents since it will be their first but how do you tell someone they're getting a third grandchild? our first baby, their third grandbaby... I know they will be just as excited but I'm not sure how to tell them. any ideas?