A new study of Colorado birth records shows that infants with low Apgar scores - the widely used measure of newborn health - are 10 times less likely to receive an initial hearing loss screening than babies with normal scores. Yet these babies are at greater risk for the most common birth defect: hearing loss.

"While the data do not suggest why these babies are missed, we can clearly conclude that clinical measures showing poor health are strongly associated with both missed screening and risk of hearing loss," said lead study author Mathew Christensen, Ph.D.

Christensen is the program evaluator at the Colorado Department of Public Health and Environment. He and his colleagues analyzed more than 200,000 state birth records from January 2002 to December 2004.

The study appears online and in the December issue of the American Journal of Preventive Medicine.

Ninety-eight percent of the infants received hearing screening a day or so after birth, but the 2 percent who did not undergo screening were likely to be those who needed it most. Moreover, of those who had a positive test - indicating loss of hearing - 18 percent did not receive timely follow up, which is a function of individual hospitals' outreach programs.

Such tests are the standard of care in the United States and 42 states require them, according to the Web site of the National Center for Hearing Assessment and Management.

Study co-author Vickie Thomson, Ph.D., director of newborn screening programs at the Department of Public Health and Environment, said that newborns' hearing is tested while they are resting or asleep and involves sending a signal of clicks and then measuring the reaction of the inner ear or brain to the sounds. Testing usually occurs four hours or more after birth or the next day.

Thomson said that her experience as an audiologist leads her to conclude that many small or low-Apgar babies could be too involved in other procedures or discharged too soon for clinicians to perform the test.

Karl White, Ph.D., director of the National Center for Hearing Assessment and Management at Utah State University, said this finding is not surprising but is important: "Basically, it says sick babies are less likely to get screened."

According to the researchers, studies show that intervention by age of six months results in a return to near-normal ability to develop speech and language.

"If hospital administrators would recognize that hearing screening is important and do something as simple as putting a check-off for this test on their discharge form," White said, "it would increase the probability of all babies being screened."

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Christensen M, Thomson V, Letson WG. Evaluating the reach of newborn hearing screening in Colorado. Am J Prev Med 35(6), 2008.