HUNDREDS of babies with hearing problems may be misdiagnosed because many parents do not know their family history or refuse during routine newborn hearing tests to disclose that they have sexually transmitted diseases, a study has found.

The NSW Statewide Infant Screening-Hearing program has screened more than 100,000 newborns since it started five years ago, reducing the average age of babies getting hearing aids from 22 months to 3.8 months.

But many are still slipping through the net because the scheme relies on parents providing information on possible risk factors, the co-author of the study and manager of the program in South East Sydney, Christine Rhodes, said yesterday.

About 95 per cent of newborns are tested within the first few hours of birth using auditory brainstem response technology. Electrodes are attached to the baby's skull and record nerve responses when sounds are whispered through ear muffs. If babies fail after two attempts, or they pass but have a risk factor, they are referred for further testing.

About one baby in every 1000 is diagnosed with a serious hearing loss. But Ms Rhodes said only about 3 per cent of parents admitted to having one of the eight risk factors associated with permanent hearing loss, when the real figure was closer to 10 per cent.

Risk factors include a baby baby born before 38 weeks or weighing less than 1500 grams, having cranio-facial abnormalities, spending five days or more on a ventilator, a family history of childhood hearing loss, or a mother having had rubella, cytomegalovirus, herpes and bacterial meningitis.

The study, published in the Journal Of Paediatrics And Child Health , found many parents did not return for follow-up testing.