Dinnigan will be 47 when she gives birth in November, and says she feels very lucky that she fell pregnant at her age.
However, Dinnigan has warned women not to leave pregnancy too late, she told Fairfax newspapers.
"I have so many friends who are trying to have children and they can't. It's your body's natural clock. You're note meant to have children in your 40s and 50s," she said.
Dinnigan said she tried IVF treatments for several years, but then switched to a combination of vitamins, exercise and health choices to help her conceive naturally.
Dinnigan married Bradley Cocks, 36, last year. She already has a seven-year-old daughter with her former husband Richard Wilkins.