The reality star was joined by about 30 guests including former Hills co-stars Stephanie Pratt, Heidi Montag and Spencer Pratt for the shower in West Hollywood, reports Us Weekly.
"Kristin was glowing and gorgeous. She looked so happy!" a source said. "Guys were there, too. It was co-ed."
The gender of Cavallari's baby was revealed earlier this month by Cutler's Chicago Bears teammate Earl Bennett, when he said the couple are expecting a boy during a radio interview.
Cavallari and Cutler were reportedly unhappy about the revelation as they wanted to keep the baby's sex a secret.
A source claimed: "They are not happy that something so personal was revealed on a radio show, especially Jay. He didn't want anyone to know what they were having."
Watch a trailer for the final season of The Hills below: