The 39-year-old actress - who has three sons, seven-year-old Dashiell John, four-year-old Roman Robert and eight-month-old Ignatius Martin, with husband Andrew Upton - admits she has been stunned each time she has found out she is expecting.
She said: "My pregnancy with Ignatius was surreal. He was a surprise. But they've all been surprises. We didn't get married to have children. So when they've popped along it's been 'whoops!' but it's been great."
Cate also revealed despite having an Oscar under her belt for her role in 2004 movie 'The Aviator', she still has to turn down roles she would have liked to take because of her family commitments.
She added to Canada's Toronto Star newspaper: "You can pick and choose as much as a mother can pick and choose. I have three kids, two of them are in school, and my husband and I are running a theatre company. I have a few months off a year, and films can't always wait."
Cate recently revealed she thinks it is her "responsibility" to have lots of children because she is "halfway decent-looking".
She said: "The world is so massively overpopulated, but if you're halfway decent-looking and you make nice ones, then I think it's probably your responsibility to make more. That's why we just have to have more of them!"