More than 1500 children will be recalled to have their hearing checked after it was found they were incorrectly screened in Hawke's Bay.
Parents will be sent letters over the next 12 weeks offering rescreening appointments.
The number covers 747 children incorrectly screened since 2008, and a further 777 babies born in the past six months.
Hawke's Bay District Health Board paediatric clinical director Philip Moore said: "We have been overly cautious and are recalling all babies screened in the past six months as well, as we can't say for sure that they have been correctly screened."
There was a low chance of a baby with a congenital hearing loss being missed, he said.
Babies who had either been admitted to the special care baby unit, were born prematurely, or who had a known risk of congenital hearing loss, were given a different screening, so they were not at risk, and not part of the recall.
The number of children needing rescreening in Hawke's Bay was high because it was the first DHB to begin the programme, and had three staff screening about 120 babies each month.
They were found to have not been testing the babies' ears correctly, and potentially missed detection of hearing loss.
The 1500 cases are in addition to the 2000 babies being recalled for newborn hearing screening after an investigation by the National Screening Unit.
It found screeners at six DHBs had not carried out screening correctly. Waikato and Hawke's Bay DHBs were not included because they were still doing audits when the findings came out. Waikato DHB will offer rescreening to 373 children.
Concerned parents should see their GPs or WellChild Tamariki Ora provider, or call 0800 643 745 for more information.
- The Dominion Post
Testing drugs on animals is:Related story: Animal tests 'key' to brain disease cures