a bun in the oven

euphemism An unborn child growing in one's womb. You're having a baby shower for Carla today? Wow, I didn't even know she had a bun in the oven. We were thinking about moving overseas this summer, but we had to shift course when we found out about our little bun in the oven. A: "Oh my gosh, you guys have another bun in the oven?" B: "Yep, and when she gets here, we'll have four kids under the age of four, which is only a bit terrifying to consider!"