Ah, this brings back memories--this is where I was exactly one year ago! Wow, time flies. So I looked up my old announcements on my Facebook page, and the day I took the pregnancy test I posted "... is thinking "holy s*&%, lions!" (this is a reference to an internet meme)
and pondering an afternoon nap in the hammock" because I was a mixture of excited, bemused, and probably a bit nervous as we hadn't been trying to get pregnant (though we were going to soon and were really happy). One friend actually guessed from this.
A couple of weeks later (I waited to a whopping 4 weeks or so because I was too excited to wait until 12 weeks), my "official" announcement was "...is pregnant with anticipation for (due date)!" which most people got, since it wasn't too subtle.