AceShowbiz - Pregnant Carrie Underwood will be forcing herself to go with the flow once she becomes a mother-of-two because she knows it will be a whole "different ball game".

The 35-year-old announced she was expecting her second child with husband Mike Fisher earlier this month.

Carrie is already mum to three-year-old son, Isaiah, and revealed in a recent interview with The Tennessean that she's well aware baby number two will change their family dynamic.

"It's going to be a different ball game, for sure," the country singer laughed. "My brain, I'm such a planner. I want to know how it's all going to go. But no matter who you are, you make it happen, you make it work, you get your team behind you."

The Grammy winner also believes Isaiah will be a great big brother.

"I think he'll be a really good big brother," Carrie mused. "I think he'll be helpful."

Despite fans speculating her unborn baby will be a girl, after Carrie wore a pink jacket in her pregnancy announcement video, the former American Idol winner is planning on the sex being a surprise.

"I don't know what it is," she said. "You've got a 50 per cent chance you're correct. I have no idea."

In a video posted on her Instagram page on 8 August, Carrie revealed the exciting news that she was expecting.

"Mike, Isaiah and I are absolutely over the moon and excited to be adding another fish to our pond," she said, after updating fans on her plans to go on tour to promote her upcoming album Cry Pretty. "We're just so excited and glad you guys can share this with us and be a part of it. Love you guys!"

Despite the baby news, the singer, who did not announce her due date, is already planning her post-pregnancy work return - she will kick off a new tour next May (19).