The photo has garnered an outpour of praise from social media, with many women applauding The Biggest Loser trainer for her 'realistic' representation of postpartum bodies.
She captioned the pic: ' Hey Arnold, this is a selfie. I am so proud of my body creating this beautiful baby boy. Arnold, my tiny knitwear model, what a joy you are.'
Her comment section was inundated by women who were incredibly moved and inspired by the fitness stars authentic representation of childbirth and the pressure women face to get back into shape.
'Showing what a real women looks like after birth,' one fan wrote. 'I had my baby 6 weeks ago and the pressure to get back into shape is real.'
'Thank you for sharing this photo,' another added. 'I'm so sick of unrealistic expectations for new mums.'
Arnold is Tiffany and husband Ed Cavalee's first child.