The HDC received 389 complaints about care provided by health boards nationally in the six-month period - the highest number of complaints ever received in a six-month period.
A missed, incorrect or delayed diagnosis was the most common specific primary issue in complaints about services.
It was the primary reason for about 20 per cent of complaints.
Failure to communicate effectively was an issue in about 34 per cent of complaints.
The report said inadequate co-ordination of care was often noted in complaints. Patients often moved from one part of the health-care system to another.
It was essential for different units to communicate well and there was a safe and seamless system to ensure the patient received appropriate care at all stages, according to the report.
On Saturday the Rotorua Daily Post reported how a 21-year-old woman had made a complaint to the health board after she suffered a miscarriage at Rotorua Hospital last week.
The woman claimed her 10-week-old foetus was flushed down the toilet by a hospital worker, denying her the opportunity to bury it with family members as planned.
The health board is investigating the incident.
