Have a bun in the oven
Definition 1 of 1
Pro Tip 1/3Idiomatic Expression
An informal, figurative phrase not meant to be taken literally. 
When Jane said she had a bun in the oven, she meant she's expecting a child, not baking.
Pro Tip 2/3Casual Context
Used in relaxed, personal settings among friends or family, rarely in formal situations. 
At the family barbecue, Aunt May whispered that she thinks Molly has a bun in the oven.
Pro Tip 3/3Humorous Tone
Often used to add a touch of humor or light-heartedness when discussing pregnancy. 
Everyone laughed when dad joked that he's getting fat and looks like he has a bun in the oven too.