Pregnant newlywed Ashlee Simpson-Wentz celebrated her 24th birthday with a 'white trash-themed' bash on Friday.

The singer, her husband Pete Wentz, sister Jessica, parents and pals all dressed up for the party at the Simpson family's Encino home.

A guest tells People.com, "It had a white-trash theme. Ashlee wore Daisy Dukes and platform flip-flops with a bathing suit and a fake tattoo around her belly.

"(Father) Joe wore a cut-off muscle T-shirt and a mullet wig. It was funny. Jessica was wearing a crazy leopard-print dress that showed off a lot of cleavage."

Simpson-Wentz is due to give birth to her first child next month.