In the cover photo released by the magazine on Wednesday, Simpson can be seen covering her breasts with her right arm and hand, and cradling her full abdomen with her left.
A photo inside shows Simpson standing as her fiancé and the father of her unborn child, pro football player Eric Johnson, kisses her belly.
Simpson, 31, revealed in October that she was pregnant with her first child, after dating Johnson since May 2010.
First taste of fame
She first rose to fame at age 19 with her debut album Sweet Kisses in 1999. She married singer Nick Lachey of boy band 98 Degrees in 2002, and the two starred together in a reality TV show about being newlyweds. They divorced in 2006.
As it happens, Lachey revealed this week that his current wife, TV personality Vanessa Lachey (formerly Minnillo), is pregnant with the couple's first child.
Doing the Demi
Simpson's cover photo on Elle is similar to an attention-grabbing nude pose actress Demi Moore, who was pregnant at the time, struck on the cover of Vanity Fair in 1991.
The Moore picture taken by renowned photographer Annie Leibovitz caused a controversy at the time, but since then a number of other pregnant stars have posed for similar shots.
Inside the magazine, she reveals that she is pregnant with a girl, confirming previous speculation.
Simpson, whose most famous acting role was in the 2005 film The Dukes of Hazzard, launched a highly successful clothing, handbag and shoe collection in 2007.