I am like NaeNae we didn't celebrate Katy's due date for us her birthdate was a day for celebration conteplation etc... and still is 6 years on
anyway I have friends who have doen balloon releases and it is majical... I dont know about formal invites etc, but maybe a informal gathering at a beach or somewhere special for your family... light candles do a balloon release Write your little ones name in the sand ...
I hope you find some peace in what you do...