Definition of have a bun in the oven Have a bun in the oven

We found 2 definitions of have a bun in the oven from 2 different sources.

What does have a bun in the oven mean?

Verb
have a bun in the oven - be pregnant with; "She is bearing his child"; "The are expecting another child in January"; "I am carrying his child"
		bear, carry, gestate, expect
		birth, give birth, deliver, bear, have cause to be born; "My wife had twins yesterday!"