Breakin all the rules

I know the rules about not talking about work in a blog.
But how else will I think things out?

I haven't told anyone at work that we're adopting. I'm not really friends with anyone so it's never going to just come up. (There's a bit of a running joke between my boss and co-workers, when the projects are getting really rough and things are going badly, they joke that they're going to have or adopt a baby "tomorrow" so they won't be in to work! So would they even believe me if I told them??) But eventually I kind of have to say something. And I've been wondering. Can they, like, fire my ass for planning to take time off?
My company doesn't have any parental leave policy. They have a short-term disability leave that you can take if you are a woman and you "have" a baby. That's more for the medical status than the parental status. So I'm planning to just use FMLA to get my 3 months off. If I declare that I am planning to, at some point in the next year or so, call in one morning and then not show for 12 weeks--can they say, um no, we're replacing you? I know they couldn't fire me if I were pregnant and said I was going to take 12 weeks off after having a baby. But that's because there's a law against firing women for being pregnant. Is there any law against firing someone for planning to take leave in the future? I know you can't be fired for USING FMLA. but could you be let go before you did? I wonder.