Jo Dee Messina is expecting her first child with husband Chris Deffenbaugh - a baby boy due in January.The 38-year-old and Deffenbaugh, 28, have managed to keep her big news secret from the world for six months.She says, "I am in my third trimester now. We knew we wanted to have kids, but we just said, 'Whenever it happens, it happens.' And it happened!"We were both surprised at first. It's such a lifestyle change. But then we're like, 'Wow, we're going to be parents!'"The star has stayed so fit through her pregnancy - she plans to run a five-mile race on Thanksgiving Day. She says, "I'll be eight months pregnant and running. It should be interesting!"