I have news...but most of the standard metaphors are kind of clunky and inappropriate. "Knocked up" makes me think of some weird zero-G mixed martial arts. "Bun in the Oven" is too Hansel-and-Gretel/cannibalish. And "expecting" makes me think that someone is never going to finish their sentence.
This is more delicate than you might think. I know that I have to maintain the dignity of the situation. On the other hand, though, I also have to communicate the joy, excitement, and potential of the event. While I am a professional writer and thus have to hunt for metaphors all the time, this one is relatively important, so I really hope this does it justice:
My spousal unit and I would like to announce that, on or about the 8th day of this upcoming June, the future master and potentate of the universe will arrive, and we, as a couple, are the responsible party...so some of the "hails" should be for us.