An independent report into a 16-year-old joy rider who killed pregnant Hobart mother Sarah Paino showed he had no mental impairment that might have excused his actions, a Tasmanian court has heard.

But Supreme Court Justice Helen Wood was also told the issues raised in the report may explain his initial lack of remorse.

The sentencing hearing of the boy - who pleaded guilty to the manslaughter of the young mother - was adjourned in June for completion of an independent report following receipt of an unsolicited psychiatric report.

The teenager was driving a stolen four-wheel drive and had run a red light at more than 110 kilometres per hours with the headlights off when he slammed into Ms Paino's car at the intersection of Davey and Argyle Streets in Hobart's CBD in January this year.

Paramedics kept the mother, 24, alive long enough for doctors to be able to deliver her baby boy.

Her two-year-old son, Jordan, who was in the back seat of the car, survived the crash unharmed.

An independent forensic medical report on the juvenile was tendered on Wednesday.

Director of Public Prosecutions Daryl Coates said there was no evidence that the teenage suffered any mental impairment.

"The report is obviously relevant," Mr Coates said.

"To a certain extent it might explain his lack of remorse.

"There's no evidence that he suffers from a mental impairment to the extent that the broader principles of general deterrents and specific deterrent don't play a factor, and in cases like this general deterrence is a major consideration."

Teenager 'should be sentenced as adult'

Mr Coates again submitted that the teenager should be sentenced on the basis of his dangerous driving across Hobart in the hours leading up to the crash, not just the crash that caused Ms Paino's death.

The court heard the teenager had switched the headlights off to evade police, and had been travelling at speeds of up to 200kph on some of Hobart's busiest roads and highways through Hobart's northern suburbs, eastern shore and the CBD.

Ms Paino's car after the fatal crash in Davey Street, Hobart. ( ABC News )

Other motorists and witnesses told police the stolen car was "flying" and travelling "insanely fast", and that at the time it entered the Tasman Bridge headed for Hobart's CBD it was swerving in its lane, and the driver appeared in danger of crashing.

Justice Wood was told that she should proceed with sentencing on the basis that the boy's three teenage passengers neither encouraged him to go faster nor told him to slow down or stop.

He urged Justice Wood to sentence the boy as an adult.

If he is sentenced under the Youth Justice Act, the maximum he could get is two years detention.

As an adult, he would be looking at a maximum of 21 years in jail.

The teenager will be sentenced next week.