The model and American Football star have not commented on the reports, however the 28-year-old Brazilian is reportedly "ecstatic" at the news.
"Gisele will be an excellent mother," said a source. "She's always wanted kids." The baby is apparently due early next year.
Another insider added: "You know Gisele and Tom are just enjoying themselves, being married and just doing their thing... Gisele has been talking about it with friends. She says she's ready for a family."
New England Patriots player Brady, who wed Bundchen twice earlier this year, already has one son, John, from his former partner Bridget Moynahan.