Aaron Papazoglu, 19, pleaded guilty in the Downing Centre Local Court on Tuesday after the fatal crash in November.
Samanvidha Dhareshwar, 33, was walking with her husband and a child in northern Sydney when struck by a station wagon.
The station wagon had been struck by Papazoglu's sedan.
Ms Dhareshwar was taken to hospital but she and her unborn baby, due in December, could not be saved.
Papazoglu on Tuesday pleaded guilty to dangerous driving occasioning death and causing the loss of a foetus through the death of a pregnant woman.
The charges carry a maximum combined sentence of 13 years in prison.
Three further charges, including an aggravated dangerous driving occasioning death charge alleging he was travelling 45km/h over the limit, were withdrawn and dismissed.
A bail court in November was told Papazoglu had no previous criminal or driving offences.
He was accused of accelerating through an intersection when the traffic light changed to yellow.
During the November hearing, his lawyer said the Kia station wagon had stopped to let the pedestrians cross the road and Papazoglu would have been expecting the car to have completed its turn before he collided with it.
The teenager had not been using any drugs or alcohol, was not street racing and had not run a red light, he said.
"This wasn't a prolonged, intentional act. This is … a tragic outcome to a series of unfortunate events," Mr Schmidt said.
The NSW government introduced a range of new offences for causing the death of unborn babies in 2022, which increase maximum jail terms by three years to an offence where the mother is killed.
Papazoglu remains on bail ahead of a sentence mention in the District Court on September 18.
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