Ambrosio and her fiancée, businessman Jamie Mazur, are already parents to three-year-old daughter Anja.
The Victoria’s Secret model broke the news to Mazur on his birthday in September, but decided not to go public due to the fashion show looming ahead.
In an interview with US Weekly, the stunning model said her family is one of her priorities.
“Family is the most important thing for me and I'm thrilled to be adding to the family," she told US magazine.
"I'm fortunate to have a loving and supportive family,” she added. “It's a blessing that it will soon be growing."
Ambrosio flaunted her toned bod during the November Victoria’s Secret fashion show, where she carried 30-lb. lingerie accessories and looked amazing doing it too.
The Brazilian babe is four months pregnant. The child's gender is still unknown.