His later actions came to light when a woman became curious about her genetic background and researched her family tree.
Another, Rebecca Dixon, whose parents had gone to Barwin to help them conceive, became suspicious when she was diagnosed with a genetic condition neither her mother nor father shared. A DNA test confirmed Barwin as her father.
Dixon, 28, told the hearing she felt "repulsed" and "contaminated" when she discovered the fertility doctor was her biological father.
"In that moment, my life changed forever," she said in a victim impact statement. "For a while I felt dissociated with my own face, as if the person looking at back at me in the mirror wasn't fully me anymore."
Her family are suing the doctor.
Her father, she said, "had to learn to accept that the daughter he had raised and loved was not in fact his biological child."
She added: "My mum had to work through the fact that something had happened to her body without her knowing, or giving permission."
So far she has discovered she has 15 half-siblings but expects the number to grow.
The claims date back to the Seventies and include patients from at least two fertility clinics in Ontario.
Barwin did not appear before the disciplinary panel but pleaded no contest through his lawyer.
