The 46-year-old "Die Another Day" star took everyone by surprise when she announced her unplanned pregnancy in April, reported Daily Express.
"That kind of coloured what my involvement could be, which was why I was one of the first ones in and the first ones out," she said.
"My ever-growing belly was posing a constant challenge. What I could do was getting more limited so the role that I play is so different from what it could have been, due to my surprise pregnancy," she added.
"There's no secret, I've just lived a healthy lifestyle. I only work out like three times a week, 30 minutes a pop. That and good clean living. As I'm getting older it is just paying off," she added.
The actress is expecting her first child with husband Olivier Martinez, and also has five-year-old daughter Nahla from her previous relationship with Gabriel Aubry.
