Ciara and Russell Wilson are the proud parents of a new baby girl ... the couple's first child together.

The singer and Seattle Seahawks QB both posted a photo of a pregnant Ciara Saturday welcoming Sienna Princess Wilson with the caption, "No matter how big the wave, we will always be your calm in the storm. We love you." Sienna came in at 7 lbs and 13 oz. 

The baby is Russell's first and Ciara's second ... she's got a 2-year-old son with rapper Future