Talking to birth moms

I've known a lot of birth moms, but I've gotten to know them through my work in adoption, which means that I know that they're birth moms right off the bat, so there's never been a time that I've "found out" that they're birth moms and needed to respond to that piece of information. However, I've sometimes wondered what to say when someone says, "I'm a birth mom." I've thought through a number of responses and worried that they're all potentially offensive. A positive response would assume that they're happy with their decision; a sympathetic response would assume that they're not. Right now "I think birth moms are the bomb" is the best one I've been able to come up with, because it says I think they're awesome without really making a judgment statement about their specific adoption story. Then with follow-up questions, I'm again stymied. Is it appropriate to ask how they feel about their adoption? If they're in contact with their placed children? What do you think?