Former midwife Lisa Barrett has been found not guilty of two counts of manslaughter over the deaths of two babies during home births in 2011 and 2012.

Key points: Ms Barrett pleaded not guilty to two counts of manslaughter over the deaths

Ms Barrett pleaded not guilty to two counts of manslaughter over the deaths Justice Ann Vanstone on Tuesday said her actions did not amount to criminal negligence

Justice Ann Vanstone on Tuesday said her actions did not amount to criminal negligence The prosecution had argued the babies would have survived if not for her involvement

Ms Barrett, 52, stood trial in Adelaide's Supreme Court before Justice Ann Vanstone without a jury.

The prosecution argued Ms Barrett was grossly negligent in the advice she gave the mothers and failed to inform them of the developing emergencies which required urgent hospital transfers.

However, Justice Vanstone found while Ms Barrett's conduct fell short of a competent midwife, it did not amount to criminal negligence.

Last year, Ms Barrett pleaded not guilty to two counts of manslaughter over the deaths of the two babies.

The prosecution argued they would have survived if not for Ms Barrett's involvement.

The claim was rejected by Ms Barrett's defence lawyer Scott Henchliffe SC, who told the court "the direct causes of their deaths were not acts of the accused or her omissions".

Sarah Kerr's son Tully died two days after his birth in October 2011.

Tully's twin sister, who was delivered first, survived.

A photo of Lisa Barrett from the time of the infant deaths. ( ABC News )

Ms Kerr previously told the court that Ms Barrett appeared calm and did not convey to her the "extreme danger" her son was in during labour before a decision was eventually made to transfer her and the child to hospital by car.

Justice Vanstone said she was satisfied that the prosecution had failed to prove Ms Barrett's acts or omissions had caused Tully's death.

"I am satisfied beyond reasonable doubt that, although unregistered, the accused held herself out as having the skills of a midwife and took on the role of midwife in respect of the pregnancies," she said.

"She therefore, owed a duty of care to each baby.

"On count one, the prosecution has failed to prove that the accused's acts or omissions in the antenatal period, or during the labour, caused Tully's death.

"In addition, I have found that the prosecution fails on proof of criminal negligence."

Judge says prosecution failed to prove both counts of manslaughter

She said while she found the accused's conduct less than competent, the prosecution had also failed to prove Ms Barrett's fault in the death of the second baby.

"On count two, the prosecution has failed to prove that the accused's acts or omissions in the antenatal period caused [the second baby's] death," she said.

"While I have found that the accused's conduct in relation to the labours of both women fell short of that of a reasonably competent midwife, in neither case has it been proved beyond reasonable doubt to be grossly or culpably negligent as the law of manslaughter by criminal negligence requires.