The 26-year-old singer posted the picture yesterday (30 October), with the caption, "Me, bump and pumpkin, i did it last night during x-factor."
She then added a close-up of the pumpkin (above, second photo), saying, "ok so i did use a stencil, but still pretty cool, no?"
Allen is due to give birth to her baby next month. She and husband Sam Cooper, 32, married in a country ceremony in Gloucestershire earlier this year.
Under the handle @MrsLRCooper, the expectant mum has kept her fans updated with regular tweets throughout her pregnancy.
"En route to baby shower, bit scared!" she tweeted earlier this month. She also said her husband her dubbed her "little Fat Controller."
Her latest photo (below) got the seal of approval from fellow pop star Cheryl Cole, despite a long-running and much-hyped feud between the pair.
"@MrsLRCooper looks ridiculously cute with her baby bump.. Aahhh..," the Girls Aloud singer tweeted.
We couldn't agree more - enjoy the photos, above and below...