The 32-year-old, who gave birth to her third child Leonardo on Tuesday 13 September 2016, shared a collage of four photos.
“Staying with the purpose of showing getting back into shape post-baby, I wanted to create a little photo show for you,” she wrote.
“In order: the last pregnant belly photo I had a week before I delivered. Then I have my 24-hour post baby hospital pic that I shared last week.
“Carmen posed with me for my one week post delivery shot today. Then the little man himself, as we left the paediatrician today.”
Baldwin was thanked by fans for sharing her progress and being honest about what a “real” body looks like after giving birth.
“You have inspired me to embrace my belly since having my daughter,” one mother wrote.
“I know other women are going through the same as me now!”
Baldwin, who is a former yoga teacher, shared her first post-baby selfie just 24 hours after birth.
She said she was “nervous” about sharing the photo, but felt it was important for her to normalise what a “real body” looks like.
The mum and her husband Alec Baldwin are also parents to three-year-old Carmen and 14-month-old Rafael.
The dad has also taken to Instagram to share photos of his family addition.
“Everyone’s here,” he wrote alongside a photo of his three children and wife.