Bun in the oven is an informal slang expression, used to describe a woman as pregnant.
While oven has been used to refer to women’s wombs since the 17th century, “bun in the oven” didn’t emerge until the middle of the 1900’s.
It is unclear where exactly the expression originates from, however, one of the earliest cases of its use come from the 1951 book of Nicholas Monsarrat, titled “Cruel Sea”.
Today it is still debated whether he coined the phrase or not.
“Bun in the oven” quickly caught on, being adopted by English speakers both in the US and England, as well as the rest of the Anglophone world.
It can be encountered frequently both in everyday conversations as well as movies and television series.
The phrase was first defined on Urban Dictionary in 2003.