Best surprise announcement for first time grandparents

What is a good, unique way to announce we're pregnant at family dinner?? So I just found out I'm pregnant, only 4 weeks. Super early but my parents have a trip planned to visit me for my birthday in 2weeks. I had previously arranged for my parents and my husbands parents and spouses to come over for my birthday dinner. The dinner is feb 17th at which I will only be 6weeks. Even tho it's not recommended to tell people before 12weeks I'm going to do it. My husbands parents are already grandparents but this will be the first for mine. Should I tell my parents separately since it's their first time? Or wait and do it when all 6 of them are over for dinner?