The phrase "bun in the oven" is an English idiom referring to a woman who is pregnant. The origin and first use of the term are unclear, but it has become a common saying in many countries that use English as the primary language, particularly in the US and Great Britain. Pop culture references to this phrase are rife.
While the precise origin of this slang phrase is unknown, it appears to have been in use since the early or mid-20th century. Literary references go back as early as the 1950s. Use of this phrase to refer to being pregnant began to appear in movies, television shows and other pop culture mediums somewhat later.
Needless to say, a woman is not a kitchen appliance. The phrase "bun in the oven," however, makes a clear comparison. In this analogy, the unborn baby is the bun and the mother's womb is the oven. The father of the child is sometimes referred to as the chef, an analogy some may find offensive.
"Bun in the oven" might have originally stemmed from certain points of comparison between pregnancy and baking. Baked items, like unborn children, must be incubated for a specific length of time. Both grow during the incubation period. Whatever the basis, the phrase appears to have become an accepted and largely inoffensive way of saying that a woman is pregnant.
This particular phrase has become so popular, in fact, that creative costume websites suggest using it as a basis for Halloween costumes. Some sites suggest decorating a large cardboard box like an oven, then cutting holes in the box for the woman's arms, legs and head. A picture of a bun, loaf of bread or muffin is glued to or drawn on the "door" of the oven. Other sites offer commercially-made versions of this costume. In some cases, the sites recommend that the woman's partner wear a chef costume.
Many other slang phrases for pregnancy have come into common use. In addition to having a "bun in the oven," pregnant women may be said to have "joined the pudding club," to be "in the family way," or to be "on stork watch." Modifications of the word "pregnant" include "preggers," "preggo" and "pg." Gentler terms include being "with child" or "expecting." Other terms include "knocked up" and, in the case of an unexpected or unwanted pregnancy, "in a fix" or "in trouble."