The 43-year-old 'No Doubt' frontwoman, who already has two kids- Kingston and Zuma with Rossdale, is reportedly expecting her third child, reported Contactmusic.
"She and Gavin couldn't be happier," a source said.
The couple begun dating in 1995 and exchanged vows in 2002.
The star, who has her own fashion line, previously said that being a mother requires one to be selfless.