"She's got a bun in the oven"
"Oh my god! Is she really PG?"
"When is she due?"

after sleeping with joe, she realized that she might have one in the oven.

1)she's got a bun in the oven (= she's pregnant)
2)they've got a bun in the oven (= they're an item and she's pregnant)
3)i've got a new application in the oven (=i'm working on some new software)
4)i've got a new project in the oven (=i'm working on a new project at the office, that is, in my day job)

Susan has one in the oven. Molly is baking twins in the oven.

Mary has a little bun in the oven. I hope it isn't mine.

My mother had twins in the oven.

1. I knocked up my bitch, now she gots a bun in the oven.
2. shit, son, I got a bun in the oven