"Mother, baby and family are all happy and healthy," he said in a statement.
The pop star and fashionista already has one son, Kingston, with her husband, rocker Gavin Rossdale. Rossdale also has a teenage daughter with fashion designer Pearl Lowe.
Stefani has racked up numerous hits and best-selling albums over the years, not only as a solo artist, but as the front woman for the band No Doubt. But the 38-year-old has also become a successful designer with her L.A.M.B. and other clothing lines.
Her last album, "The Sweet Escape," was released in 2006, a follow-up to 2004's multiplatinum "Love. Angel. Music. Baby."