Leah Gayo was at the end of a routine pregnancy when she arrived at Auckland City Hospital on April 20 to deliver her second child. But the 32-year-old suffered a heart attack in labour and, despite efforts to resuscitate her, she died in childbirth.
Her son, Leandro, was safely delivered by emergency caesarean.
Mrs Gayo's case was among 489 serious adverse events at hospitals and health centres last year.
In 82 cases, patients died, but not necessarily because of the incident.
In one mix-up, a cardiac procedure was carried out on the wrong Waikato Hospital patient. The incident involved two patients with the same surname in the cardiac ward.