The couple went on Instagram to announce the good news right before 2015 rolled in.
In their post, the 30 year old yoga instructor shares an image of the family with their eldest child, Carmen Garbriela, who is 16 months old reaching out for her mother's belly, against a stunning beachside backdrop:
"The sun has set on 2014," the yoga instructor, 30, captioned a precious photo of the couple and their little girl. "2015 is going to be very exciting as we are thrilled to announce we are expecting another little addition to our family!"
She also takes to Twitter to announce an upcoming addition to their family.
"2015 equals Mommy, Daddy, Carmen and a special guest star...."
Baldwin also has a teenage daughter, Ireland, who is 19 years old from a previous marriage to Hollywood actress, Kim Basinger.