The actress, now 22, shared a role with her twin sister Ashley on the family TV situation comedy "Full House," then later co-starred with her sibling in a string of popular tween- and teen-targeted, made-for-video movies.

The sisters now have their own fashion line and recently released a style-themed coffee-table book.

The National Enquirer quoted a source as saying: "Mary-Kate has been looking a lot rounder recently. It is good she has put on weight, because she previously suffered from anorexia, but a lot of people think she could actually be attempting to hide her pregnancy."

However, Olsen's publicist told Usmagazine.com Tuesday, "Mary-Kate is absolutely not pregnant."