I am beyond pissed. I have to confront him today. Grrrrrr. DH was in the hardware store yesterday morning and a local person/acquaintance yelled across the store "congratulations on the baby!". And that person confirmed that it was my boss who told him. Fuming. I haven't even told most of my dearest, closest friends yet. I have told my boss dozens of times why we aren't telling anyone until after my 12 week appointment, so I know that there was no confusion about whether or not this is PRIVATE information. Sorry this post is disjointed, I'm all worked up.
No snark intended, but just curious as to why you would tell your boss before those close to you. Do you have some very physical/dangerous job? Unless I was in danger, the last person I would tell is my boss (well... boss than coworkers)!
But PPs are right... I would likely have a conversation with my boss about it and if the behavior continued then I would go to HR. I wouldn't go directly to HR because it may be that he is genuinely excited for you and doesn't realize it's a "no no" to do this. However, you know him better than anyone on here as to what his intentions may be. GL!