Ask the Expert – Screening Newborns for Hearing Loss

This Ask the Expert article is the first of many articles provided by guest experts.

My guest expert for the inaugural installment of Ask the Expert here on boogordoctor.com is a long-time friend of mine, Dr. Kirstin Chiasson.

I invited Dr. Chiasson to provide some insight into “hearing testing” that is done on newborns – why it is done, what it can and cannot tell us, and what to do if your newborn has an abnormal screen.

For today’s topic – screening for hearing loss in newborn babies – she is eminently well-qualified:

Kirstin Chiasson, PhD in Audiology

  • Bachelor’s in Speech and Hearing Sciences from UC Santa Barbara
  • Master’s in Audiology from San Jose State U, followed by a
  • PhD in Audiology earned at U Wisconsin-Madison
  • Dr. Chiasson has been honored with several research awards
  • She has been the recipient of several Research Grants from NIH
  • Awards from the American Speech-Language and Hearing Association, as well as from the Universities that she has been affiliated with.
  • As one of those “academic types,” she has published multiple papers in medical journals, presented at multiple national and international medical and scientific meetings, and taught many workshops and seminars.   Heavy duty!
  • Dr. Chiasson is currently Director of Audiology, Cascade Ear, Nose, Throat, & Facial Plastic Surgery Center, Klamath Falls, Oregon

I was fortunate to work with Dr. Chiasson for several years, and wish I were still working with her, wish that she were providing hearing evaluations for my patients now.

I am honored that Dr. Chiasson has accepted my invitation to write an article for my blog. She has set the bar very high indeed for future guest authors on Ask the Expert.

Why are you screening my baby’s hearing?

 

Newborn undergoing screening (cutie-pie!)

 

Don’t Delay

For many years babies born with hearing loss were not noticed to have hearing loss for years. They weren’t “diagnosed” as hearing-impaired until they reached 2 or 3 years of age.

That’s too late!

Unfortunately, when a child is 2 or 3 years old the opportunity to easily learn language (spoken or signed) has passed.

There is a short “window” for the brain to learn how to process those signals and to learn language.

We need to detect hearing loss much earlier! Within months of birth!

Screening

Screening for hearing loss is simple, safe, and accurate. Any question of an abnormality on a hearing screen should lead to a more thorough, accurate diagnostic testing, and – if indicated – effective interventions like hearing aids, cochlear implants, and speech therapy.

Infant hearing screening methods – let’s call them “screeners” here – are all based on evaluations of the biological hearing mechanism – the anatomy.

There are many commercially available infant hearing screeners.

The two most common techniques are:

  • otoacoustic emissions (OAEs) and
  • automated auditory brainstem responses (aABR).

Both are painless, and can be used to test newborns and other babies who will not cooperate with other types of hearing screens. Technically, these are not tests of hearing, but simply screens for normal function of the anatomic mechanism – normal ear function.

Why aren’t they tests of “hearing”?

Hearing requires more than an intact ear. It requires everything up to and including the portion of the brain that decodes the incoming auditory signals.

To determine whether all of it is working – that we are “hearing” and “listening” – means that we would have to ask questions about the meaning of what is in those signals. That’s just not possible in a newborn or infant.

Despite the inability to test the complete hearing system in a newborn, it is important to have your newborn’s hearing mechanism tested. A normal ear is very reassuring, since most problems with hearing loss occur in the ear.

Otoacoustic Emissions

When sound is presented to the inner ear, hair cells in the inner ear fire and send a signal up to the brain. When quieter sounds are presented to the inner ear, the hair cells actually shorten. The shortening of the hair cell causes a new sound to be created. The new sound is the “echo.” A microphone in the outer ear canal can measure the echo. The baby passes the OAE infant hearing screening when “echoes” are measured in the baby’s ear canal.

Auditory Brainstem Responses

When sound is presented to the inner ear and the hair cells fire, the hearing nerve also fires. When a single cell, or neuron, fires it generates a tiny amount of electricity. The firing of many hearing neurons at the same time results in a small charge that can be measured on the skin of the baby’s head. If the computer measures electricity, the baby passes the infant hearing screening.

Screening Only Shows Us Whether The Ear is Working

There is more to hearing and listening than a working ear. Remember, screenings are not tests of listening. Screening only tests the nerve function of the ear.

Listening requires:

  • the sound to be conducted through the outer and middle ear to the inner ear hearing nerve
  • the hearing neural apparatus (cochlea and hearing nerve) must be intact and healthy
  • the anatomic brain structures that relay the signal must be intact and healthy
  • your brain must receive the hearing nerve signals
  • your brain must decode the hearing nerve signals
  • your brain must give the sound meaning
  • and finally, you must be able to respond to the sound

That’s what it means to hear and listen: to pay attention, to hear, and to respond.

The “screening” tests (OAE and aABR) only check the function of the ear portion of the system. Even though they look at just a small part of the entire system, there are many things that can cause an “abnormal, refer” result. See below.

So, My Baby “Failed” A Hearing Screening.

What Now?

If a baby “refers” on an infant hearing screening, the hospital or birthing center will provide a second screening. This is because screenings are not 100% perfect. Close, but not perfect.

Possible causes of an “abnormal, refer” screening result despite normal ears include:

  • A noisy room (common in hospitals)
  • A restless, fussy baby (like that ever happens)
  • Gook in the baby’s ears (middle ear fluid – very common, and temporary)
  • A lot of electrical interference in the room where the baby is screened (common in hospitals)

Any of these can cause a baby to “refer” on a screen even though the baby has normal hearing.

Screening programs in the United States have accuracy rates of 98% or better.

Pediatric Audiologist

If your baby “refers” on the infant hearing screening, don’t panic. But DO follow up.

Follow up: Make an appointment with a pediatric audiologist for a more thorough diagnostic evaluation.

The audiologist will review the screening results, your pregnancy history, your baby’s health history, and your family history of hearing loss.

Based on the review, the audiologist will perform diagnostic testing that will either rule out a hearing loss or define the hearing loss. (Dr. Chiasson will review how these tests are done in the next installment here.)

Profound hearing loss (deafness) occurs in 3 to 4 babies per 1000 born (less than one-half of 1%). Mild to moderate hearing loss occurs in as many as 14 babies per 1000 born (more than 1%).

It is really important to follow-up if your baby “refers” on a hearing screening.

If your baby does have hearing loss, early intervention makes a huge difference in how successful a baby is at learning language and ultimately doing well in school.

The majority of children with hearing loss that is detected early have normal lives, function well in public schools, and have normal intelligence and learning abilities.

Delayed detection of hearing loss can result in delayed development of speech and language. Nobody wants that.

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Dr Chiasson’s next installment will focus on exactly how a baby’s hearing can be tested.

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Resources

Image Credit: http://www.flickr.com/photos/blackdutchdoublelibra/

Review of “Newborn Hearing Screening” by A. M DeMichele, PhD, on eMedicine: http://emedicine.medscape.com/article/836646-overview

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