The obstetrician who assessed Caroline Lovell after she was rushed to hospital in cardiac arrest shortly after giving birth estimated she could have lost up to four litres of blood before her collapse.
Dr Adam Pendlebury was the obstetrician on call when Ms Lovell, 36, was taken by ambulance to Austin Hospital in Melbourne's northeast in January 2012, hours after giving birth to her second daughter.
Ms Lovell fainted after getting out of her birthing pool and later stopped breathing after telling her husband and midwives to call an ambulance because "I'm dying".
Her midwives Gaye Demanuele and Melody Bourne are charged with manslaughter over Ms Lovell's death less than 24 hours later, allegedly having been negligent in their care.
Dr Pendlebury said the room was surprisingly not frantic when he went to treat Ms Lovell.
"It was a bizarre situation to walk into where the patient was receiving full intensive care support with an obstetric issue," he said.
"I've never been in that situation before."
Intensive care and emergency doctors were examining her for a pulmonary embolism. Defence lawyers have suggested a rare amniotic fluid embolism as a possible cause of Ms Lovell's collapse and subsequent death.
But Dr Pendlebury said his impression was that an embolism was incorrect and a post partum haemorrhage, which occurs in about 20 per cent of births - was the correct diagnosis based on her very low haemoglobin levels.
The midwives had assessed Ms Lovell as having lost 400ml of blood during her delivery and in the birthing pool afterwards, before she fainted.
Dr Pendlebury said midwives were trained to visually assess blood loss and were "experts" at doing it.
He said most commonly it was an underestimate, but agreed with Bourne's barrister Robert Richter QC that overestimation was possible.
However, Dr Pendlebury suggested that figure was too low and he had never seen a patient collapse having lost less than 500ml of blood. Other doctors have told the committal hearing that 500ml, or one unit of blood, is what blood donors give.
"In a pregnant woman, the circulating volume is six litres and if haemoglobin is at four, down from 110 or thereabouts, you'd anticipate she's probably lost between two and four litres before collapse," he said.
Given there was no evidence of retained internal bleeding, he said he would assume the blood had been externally haemorrhaged.
Demanuele has faced Melbourne Magistrates Court alongside her lawyer, Rishi Nathwani, who is appearing by videolink.
On Thursday magistrate Peter Reardon ordered Bourne must appear by videolink with her camera on, noting she is on bail and he hadn't seen her for days.
He joked she was unlikely to be on her way overseas, but rejected a claim by Mr Richter she should be allowed to have the video off because of "certain issues about being seen by a whole lot of people".