"They've both talked about this for a while and are so excited," a source told the magazine. "Everyone is beyond thrilled for them."
The Hart of Dixie actress met Christensen on the set of Jumper in 2007 and they got engaged in 2008. The couple split in 2010 before getting back together three months later.
Bilson admitted to Cosmopolitan last May that she was seriously considering becoming a mom. "I definitely have family on the brain. Having kids is something I want to see in my future — I hope," Bilson said.
Watch Rachel Bilson talk Zoe and Wade on Hart of Dixie.