MARIAH CAREY is very close to delivering twins -- in fact, she had contractions this past weekend -- but we haven't really gotten a good look at her pregnant belly, until now.  On Monday, Mariah posted on Twitter a photo of her huge baby belly, on which she had painted a big pink and blue butterfly, along with the words "dem babies."  That's what she calls the twins.

In addition to the photo, Mariah also wrote a caption in which she described her painted belly by saying, "My attempt at festiveness on 3/27!" -- that's her birthday.  She added, "For all the Lambs in the land, thank you and I love you.  Comin' soon: dem babies!  Love ya much and thanks for making me happy!"  Mariah-watchers know that "lambs" are her pet name for her devoted fans.

Mariah and her husband NICK CANNON are expecting a boy and a girl sometime in the next month.