I am a single parent, expecting my second child. How do I announce it at work?

I am expecting my second child after 13 years!!! I know, I know. As if dealing with that isn't tough already, I'm trying to figure out the best way to announce it at work. It's inevitable, of course, everyone is going to find out eventually. But my issue is that I am one of few people who work at my job (a school) who isn't married. So I guess you could say I am a little embarred to be having another child out of wedlock. Everyone else that has been having babies is married. While it was my best intention to be married the second time around, it just didnt work out that way. I just chalk it up to life, and not being as careful as I have been in the past. This is only my second time being pregnant ( I have never had an abortion or miscarried) so I guess being responsible for the past 13 years should stand for something. But again its just the stigma of it. I don't want anybody judging me because I'm pregnant and not married, but at the same time, I'm not trying to hide it either. Just need suggestions on how I should go about this. I'd rather announce it than to have people coming up to me asking me and questioning others about it. Only my co-worker knows at this time so I don't want her to be bombarded either. I'd rather everyone get if from the source. If I was married, it wouldn't be an issue. Thanks in advance. By the way, I'm 29 years old and had my first child when I was 16 if that helps.