Dawn Graves, 25, pushed the pram, with her 20-month-old son Aidan, out of the lorry's path, but died after she was hit by the vehicle herself, an inquest heard.
She suffered multiple injuries - described as 'unsurvivable' - as she crossed a street in Bolton, Greater Manchester, in May.
The tragedy happened just weeks before she was due to marry her partner.
Deputy coroner Alan Walsh said that the mother-of-two gave no thought to the danger to herself as she pushed her son to safety.
Witness Thomas Grimshaw said he flagged down the lorry driver - who was unaware of the accident - and his partner, Rachel Bell, rushed to help stricken Dawn.
Rachel told the inquest: "She was just stepping off the pavement and she continued to walk.
"She was fiddling with what appeared to be some sweets as she pushed the pram."
She said she saw Dawn push the pram out of the way and then saw her fall to the ground. She said she thought the driver couldn't have avoided the accident.
Lorry driver Eric Hamilton, who is not facing any charges following the accident, told the court he had been heading home for a lunchtime sandwich when he stopped to allow a pedestrian to cross in front of him, but he did not see Dawn.
"I was devastated. My legs were like jelly and I had to sit down," he said.
The court heard Miss Graves had been looking forward to her wedding to her partner, Barry Guest, in August.
Recording a verdict that Dawn's death was a result of an accident, Mr Walsh said that she had 'sacrificed her own life for the benefit of her son' and recognised the terrible scene that had met the witnesses.
He said: "I believe what happened was horrific for the witnesses. Dawn suffered unsurvivable injuries."