The 31-year-old singer-turned-fashion designer - who is expecting her first child with fiancé Eric Johnson - celebrated her impending arrival in Los Angeles on Sunday.
Actress Jessica Alba and Jessica's little sister Ashlee attended the bash, which was organised by celebrity event planner Mindy Weiss.
According to People Magazine, Jessica dressed prettily in a light blue dress with her hair down and soft braids around her face.
A source said: "Jessica looked pretty and very happy," while a second added: "She's so excited to be a mom. She can't wait to meet her little girl."
Meanwhile, Jessica says she would like to design her own maternity line, although she is struggling to come up with something original.
She told USA Today: "I've started to try to come up with designs. I haven't loved anything. I was going to launch a maternity line, but it seems like everything being made is already out there.
"I really want to make a maternity line that is comfortable but really stylish. It's a little bit harder because people don't what to spend a lot on maternity clothes because you're pregnant for almost 10 months. It's a harder business but I want to do it eventually."
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