It also heard that Ms Nathan's midwife's clinical notes appeared to be lacking when she arrived at Waikato Hospital.
Waikato Hospital anaesthetist Dr Aidan O'Donnell said Ms Nathan was haemorrhaging severely having lost two litres of blood.
"She was a class 4 haemorrhage which is the most severe...I believed the haemorrhage was the sole cause of her condition at the time."
Dr O'Donnell said it appeared Ms Nathan had lost more blood than what had been described in the clinical notes that came with her.
He was told she had lost 1 to 1.5 litres of blood but if that was the case she would have responded well to blood transfusions.
"Casey in my opinion had not lost enough blood for how sick she appeared to be. The other manifestations are explained by amniotic fluid embolism AFE - in other words this was not just a haemorrhage."
AFE is a rare and unexpected complication when it's believed amniotic fluid, fetal cells, hair or other debris enter the mother's circulation and cause cardio-respiratory collapse.
"It (AFE) is like a bush fire, once it has taken hold, you can only attempt to keep the flames out and prevent it from spreading," said Dr O'Donnell.
Asked by Coroner Garry Evans if Ms Nathan arriving at hospital earlier would have helped diagnose her AFE, Dr O'Donnell said it was possible.
"I'm reasonably sure that if we had access to Casey earlier then we would have considered AFE as a possibility."
The inquest, which is set down until next Monday, heard how Kymani suffered brain damage during delivery.
