The 37-year-old died from multi-organ failure caused by the infection within hours of delivering her baby stillborn and less than 24 hours after falling ill in August 2017.

Another obstetrician earlier prescribed rest and paracetamol when she reported gastroenteritis symptoms, but when her condition didn't improve Ms O'Brien went to Holmesglen Private Hospital.

When her membranes spontaneously ruptured at 18 weeks, she was urgently transferred to St Vincent's Private Hospital where her own obstetrician Dr Vicki Nott was expected to meet her.

Dr Nott arrived about 1.30am - more than an hour after Ms O'Brien - and immediately diagnosed sepsis.

She told an inquest into Ms O'Brien's death on Thursday that there was a golden hour - a principle that antibiotics should be administered within an hour of a diagnosis of sepsis.

Dr Nott admitted initially prioritising the delivery of the baby over administering the antibiotics, but when the birth wasn't imminent she wrote up a prescription at 2am.

Ms O'Brien delivered the baby at 2.12am and didn't receive her first dose until 2.46am.

The drugs were only given then when midwife Raechel Miller, who had been at Ms O'Brien's side since her arrival at 12.15am, noticed the syringe sitting on a bedside table.

She didn't know who ordered it or who put it there, but immediately questioned Dr Nott about whether it should be given and then administered the dose.

Ms Miller said she questioned when Ms O'Brien arrived if she should even be there because she was so unwell.

"We would not normally have a patient appearing like that on the ward. I was wondering in my mind is this the place Annie should be," she said.

Nearly an hour later Ms Miller found a syringe containing a dose of a second antibiotic that had not been given.

Ms O'Brien had already been transferred to theatre by then, said Ms Miller who wasn't aware the drug had even been ordered.

Ms O'Brien's father, retired GP Brian Moylan, acknowledged the distress the young midwife had experienced caring for his daughter.

Ms Miller has since changed careers.

"Personally the impact of this event means that I have been unable to continue working as a midwife or a nurse, despite my efforts to do so," she said.

"It was an incredibly traumatic experience."

In an expert opinion, Professor Mark Umstad said Ms O'Brien was displaying the classic symptoms of sepsis, describing delay in giving antibiotics as unexpected.

"Given that Mrs O'Brien was clearly septic and unwell I am unable to determine any reason for the delay," he wrote in a submission to State Coroner John Cain.

Materno-fetal medicine specialist Dr Lucy Bowyer also found there was a failure to deliver antibiotics swiftly enough at St Vincent's.

The inquest is set to continue on Monday.

Australian Associated Press