I guess since I got such quick negative input I should add that we are donig this because it is the first grandbaby/greatgrandbaby of BOTH sides of the family and after having a hard time the first time around. So we are excited to know what our babies genitalia will be and would love to annouce it! Seems to me like not a lot of other peoples family cared about the gender..
So you didn't get the response you were hoping for, huh? You asked for opinions and we gave ours. It's selfish to think that your unborn child is the center of anyone's world and needs a party to reveal it's sex. Do it or don't do it (it sounds like your mind was made up before your original post) but know that many people think it's in poor taste, is tacky and AWish. If you're fine being that type of person then by all means go for it.
Oh and it doesn't matter if this is the first, fifth or twentieth grandchild on both sides, it's still tacky.
Also, genitalia is a real word. Just like sex, penis and vagina are. If you aren't mature enough to say or type those words then you're not mature enough to have a child.