Two other Wanganui cases involved elderly male patients who fell and fractured their hips. Details around the final Wanganui case cannot be made public due to coroner's suppression orders.
DHB chief executive Julie Patterson said all incidents were investigated thoroughly.
"We are pleased that this is a significant improvement on the nine events in the 2010/11 year.
"The findings of investigations are shared with the patient and/or family.
"Any recommendations to prevent that harm happening again are implemented," Mrs Patterson said.
"Our falls prevention programme is also intensive and I do believe that the drop in the number of incidents reflects how hard WDHB staff are working to improve the care and safety of our patients."
Nationally, 360 serious and sentinel adverse events were reported in the 2011/12 financial year, down from 370 in the previous year.
Ninety-one of these cases resulted in patient deaths, compared to 86 in 2010/11.
Commission chairman Alan Merry stressed not all reported events were preventable, but many involved errors which should not have happened.
Falls continue to make up the bulk of serious and sentinel adverse events in hospitals, accounting for 47 per cent of all cases.
However, nine patients had surgical instruments or swabs left inside them and 10 others underwent the wrong procedure or treatment.
There were also 18 reported mistakes with patient medication. APNZ