The 27-year-old singer is already mother to three-year-old daughter Alaia-Mai with her former JLS star spouse.
The Saturdays star Rochelle announced that the couple are preparing to welcome a new arrival into their lives, reported Daily Mirror.
Sharing a stunning black and white picture of her wearing a sports bra and white shirt draped over her shoulders, Rochelle is seen cradling her already prominent bump.
Admitting she and Marvin have yet to find out the sex of their unborn baby, Rochelle captioned the shot on Instagram: "Ten tiny fingers, ten tiny toes, but who are you? Nobody knows...