Count the Toes, Test the Ears
Of all the congenital problems for which babies can be tested, abnormal hearing is the most common. Two to four babies per 1,000 enter this world with significant hearing impairment, making the condition 20 times more frequent than phenylketonuria, a metabolic problem for which newborns are routinely screened.
Yet estimates for the average age at which a serious hearing impairment is diagnosed range from 14 months to 2 1/2 years.
This may sound early enough. It’s not.
“In the past, we haven’t really appreciated that even when babies were just lying there, a few weeks old, their brains were already developing the capacity for language,” says Jim Battey, director of the National Institute on Deafness and Other Communication Disorders, in Bethesda, Md. “If they receive no language input during a critical window of time--a time that stretches back to birth--they lose an opportunity to learn language.”
Thus, while early detection gives a child a good chance of communicating normally (either in sign or spoken language) by the time he or she begins school, late detection and intervention mean a child has a long, dreary game of catch-up ahead. (And some kids never can catch up.) In studies of preschoolers, those whose problems were detected after 6 months of age were more likely to have developmental delays than those whose problems were detected earlier. They lagged behind in their ability to use and understand expressive language; in their social and emotional growth; and in the scope of their vocabulary.
This doesn’t mean there’s no hope if a child’s problem is discovered late, says Christine Yoshinaga-Itano, professor at the University of Colorado at Boulder and lead author of the studies. “But it’s harder.”
Which is precisely why hearing advocates have been pressing for across-the-board screening for hearing problems in newborns.
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“Screening is extremely important--especially right now, given the baby boomlet surge that the U.S. is experiencing,” says Jim Potter, director of government relations for the American Speech-Language-Hearing Assn., a professional group that advocates early screening. “We want to give children every chance that we can.”
Such advocates are making headway. Today, 24 states have enacted legislation for universal newborn screening programs--twice as many states as a year ago. Legislation is pending in at least a dozen states to establish or build on existing laws.
And last year, Congress passed a bill, sponsored by Rep. James T. Walsh (R-N.Y.) and signed into law, to provide grants to help states set up screening programs and provide the necessary follow-up care.
In California, legislation signed by Gov. Pete Wilson in 1998 requires that screening be offered to newborns in more than 200 California hospitals by Dec. 1, 2002--a move that would cover 72% of the state’s newborns.
It’s relatively straightforward, of course, to test the hearing of an adult: Audiologists simply put people in a booth and have them press buttons and parrot back phrases in response to the sounds they hear. It’s another matter to test the hearing of a baby.
Luckily, if a baby’s mouth can’t tell you, his or her ears can do the talking instead, due to an odd property of hearing that has only been appreciated in the last few decades. Ears, it seems, not only receive sounds, they emit them as well.
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The source of these sounds are “outer hair cells” in our ears that move around in response to noises, somehow sharpening our hearing. As a byproduct, the movements vibrate the eardrum, sending noises back out into the world.
Sometimes, rarely, these sounds can be spectacularly loud. Mario Ruggero, a neuroscientist at Northwestern University in Evanston, Ill., recalls meeting a woman who had hums emanating from her head, and has done studies on a dog that emitted sounds “in the 60-decibel range”--about the level of a normal human conversation.
But these are Ripley’s-worthy peculiarities. The noises an ear normally makes when exposed to sound are so quiet we don’t even hear them. They’re loud enough for instruments to detect, though--unless, that is, there’s significant hearing impairment. Then the outer hair cells don’t jiggle. The sounds aren’t generated. And that is the essence of a main way to screen for hearing problems in newborns.
In a procedure that takes just a few minutes, technicians send a click of sound into a baby’s ear, and a little microphone detects any sound coming out. The test can detect anything from mild to profound hearing loss.
In California, if all goes smoothly, screening will begin by early March at some centers, says Dr. Marian Dalsey, coordinator of the state’s screening program, at the California Department of Health Services. When fully up and running, it’s estimated that the program will identify 1,200 California children with hearing loss each year.
