People.com said Simpson and Wentz, who married earlier this month, announced on Wentz's site friendsorenemies.com that Simpson is pregnant with their first child.
"While many have speculated about this, we wanted to wait until after the first trimester to officially confirm that we are expecting our first child," the newlyweds wrote. "This is truly the most joyous time in our lives and we are excited to share the happy news and start our family."
Simpson has legally changed her name to Ashlee Wentz but will be known as Ashlee Simpson-Wentz professionally, People.com said.
Celebrity Couples of 2014 [PHOTOS]