Definition of have a bun in the oven in US English:

have a bun in the oven

phrase

informal
  • Be pregnant.

    • ‘Once Bening successfully has a bun in the oven, Shandling's work is done, so he becomes the typical lazy husband, not interested in sex or talking.’
    • ‘This chick, who's like a soapie star in Australia - announced six weeks ago that she had a bun in the oven.’
    • ‘Which Big Brother brunette has a bun in the oven?’
    • ‘It was still a bit strange that I was not yet twenty but still had a bun in the oven.’