A pathologist has told the Wellington Coroner's Court that a baby who died in 2008 was suffering from a rare congenital defect in his diaphragm which would have been difficult to diagnose.
Rhys Foaese's mother earlier told the court she had called a telephone helpline four times in the hours before the 21-month-old died in July last year.
The baby had a sore stomach and had vomited repeatedly in the hours before he died.
Three HealthLine nurses told his mother to give him small amounts of water as it was likely he had a stomach bug and the fourth suggested that she take him to the doctor if he did not improve.
Soon after that, the baby's condition deteriorated rapidly and he died a short time later.
Pathologist Jane Zuccollo told the court the boy had had a recent viral infection but the congenital defect was the underlying cause of his illness.
The Coroner has reserved his decision.