Credit: Kevin Mazur/WireImage

Mom-to-be Mariah's got butterflies on her tummy--literally!

While celebrating her 42nd birthday on Monday, Mariah Carey posted a twitpic of her painted baby belly, festooned with a huge, colorful butterfly.

"My attempt @ festiveness on 327" she wrote in the caption.

The day before, the singer, who is expecting twins with hubby Nick Cannon, started having contractions and was taken to the hospital-- but it was a false alarm. "They almost came on 3/27 - happy anniversary indeed!!! We have a few more weeks 2 go but - wow!!!:)"

She added: "so ready already!"