Over the last month or so, I've designed and listed several printable birth announcement designs. As I was coming up with the designs I had to think about the kind of wording that would go on a typical announcement. And that's the thing, there isn't a typical announcement, or at least there shouldn't be.
Just as on a wedding invitation, the birth of your baby is a special, personal milestone. Yes, you want to make sure that the big stats are listed: birth date, weight and name, but other than that, it's totally up to you.
A quote, poem, personal note, just the relevent details, the main thing is that it should feel right to you.