Prosecutors have told an inquiry examining the convictions of Kathleen Folbigg there may be "reasonable doubt" to her guilt.

Folbigg was jailed in 2003 for the murders of her children Patrick, Sarah and Laura - aged between eight months and 19 months - between 1991 and 1999.

She was also found guilty of the manslaughter of her firstborn child, Caleb, who was just 19 days old when he died in Newcastle in 1989.

Folbigg, now 55, has always insisted that their deaths were from natural causes and has petitioned for a pardon from her convictions.

The convictions are currently subject to an inquiry, which has heard new scientific evidence that prosecutors now say may support her claim that the deaths were from natural causes.

On Wednesday, New South Wales state director of public prosecutions Sally Dowling made a written submission to the inquiry saying that, in light of the new evidence, it was possible there was reasonable doubt about her guilt.

The lawyer appointed to assist the chair of the inquiry also said she had concluded that on the basis of the evidence heard since November that Folbigg was not guilty beyond reasonable doubt.

If the head of the inquiry, retired judge Justice Tom Bathurst, finds reasonable doubt of Folbigg's guilt, he could recommend that the state governor pardon her.

He could also report to the Court of Criminal Appeals to consider quashing her convictions.

Folbigg's first child, Caleb, was born in 1989 and died 19 days later in what a jury determined to be manslaughter.

Her second child, Patrick, was eight months old when he died in 1991.

Two years later, Sarah died at 10 months, while her fourth child, Laura, died in 1999 at 19 months.

She was found guilty of three counts of murder and one count of manslaughter in 2003 and jailed for 30 years - a sentence that is due to expire in 2033.

However, evidence discovered in 2018 that both Sarah and Laura carried a rare CALM2 genetic variant sparked an inquiry into her convictions.

Read more:
Australian mother convicted of killing her four children petitions for a pardon
Scientists call for convicted child killer Kathleen Folbigg to be pardoned

The genetic mutation is, according to cardiologists, associated with unexplained cardiac arrest in infants and "is a reasonably possible cause" of the daughters' sudden deaths, the inquiry heard.

The inquiry also heard that there was "persuasive expert evidence" that an "underlying neurogenetic disorder" may have caused the sudden death of Patrick.

Folbigg was the only one at home or awake when the children died and she said she discovered three of the deaths during trips to the bathroom and one while checking on a child's wellbeing, jury members in her trial were told.

Prosecutors also told the jury that Folbigg's diaries contained admissions of guilt.

However, psychologists and psychiatrists gave evidence to the inquiry that it would be "unreliable to interpret the entries in this way".

Folbigg had been suffering a major depressive disorder and "maternal grief" when she made the entries, Sophie Callan, the lawyer appointed to assist former Justice Bathurst in the inquiry, said.

"This casts Ms Folbigg's expressions of guilt and responsibility for the deaths of her children in her diary entries in a very different light," she added.

The inquiry, which is hearing final submissions, has been adjourned until Thursday