An expanded study is under way looking at why some pregnant women and new mothers become so dangerously ill they nearly die.
A recent smaller study found almost 40 percent of cases assessed were preventable, with factors including delays in diagnosis and failure to recognise high-risk patients. Most were found to have suffered from blood loss or septicaemia.
Lead researcher Beverly Lawton, director of the Women's Health Research Centre at Otago University, said the issues were found at all levels of clinical staff, at all four district health boards involved in the study.
The study is now being expanded to cover nine district health boards with panels of 60 experts examining cases.
The Ministry of Health said the audit will be used to feed into maternity quality programmes.