a bun in the oven - a woman who’s got a baby growing inside her, like a surprise

a woman who’s got a baby growing inside her, like a surprise gift from a greasy restaurant

My mom is a bun in the oven. She’s been eating tacos nonstop.

She texted me, 'I’m a bun in the oven, and I’m not going to let you forget it.'

That lady is a bun in the oven. She’s got a baby in there, and it’s probably hungry.