The Victoria's Secret model, who has 16-month-old son Flynn with her husband Orlando Bloom, says her grandmother Ann, who lives in Gunnedah, NSW, was full of advice on how she should handle the pregnancy.
"She was like, 'Now, love, don't let yourself go'," Kerr told UK Vogue.
"Men are very visual and I think it's important that you wake up in the morning and get yourself together. Don't slop around the house all day in your pyjamas. It's true! They tell you, 'It doesn't matter what you wear or what you look like, I love you anyway' but they notice when you make a little effort for them."
The 29-year-old Aussie beauty has an enviably toned body, but is keen for fans to know she works hard to keep in shape. She does yoga and Pilates daily and also takes health supplements such as goji berries and aloe vera juices.
"Working 16, 17 hours, you need to know how to take care of yourself or you'll fall off the wagon. I know it's cliched but I feel health is wealth," she said.
"I was lucky for a while there, I just did yoga. Now I'm exercising a whole lot more, but it's for my job. It is a lot of work!"