It's estimated that serious hearing loss occurs in about 2 to 3 of every 1,000 newborns. Without screening or testing, hearing loss may not be noticed until the baby is more than 1 year old. If hearing loss isn't found until later years, the brain's hearing centers won't be correctly stimulated. This can affect hearing development and can delay speech and language. Social and emotional development and success in school may also be affected.

Most hearing loss is present at birth (congenital). But some babies develop hearing loss after they are born. Hearing loss is more likely in:

• Babies who are born early (premature)
• Babies with infections
• Babies with respiratory problems needing long-term use of breathing machines and certain medicines

Because of these risks, many health organizations now advise universal infant hearing screening. Today nearly all newborns are screened for hearing loss. This allows earlier treatment to prevent delays in language and development.

There are two types of hearing screening for newborns. They may be done before babies leave the hospital but should be done before the baby is 1 month old. These may be used alone or together:

• Evoked otoacoustic emissions (EOAE). This test uses a tiny, flexible plug that is inserted into the baby's ear. Sounds are sent through the plug. A microphone in the plug records the responses (otoacoustic emissions) of the normal ear in reaction to the sounds. There are no emissions in a baby with hearing loss. This test is painless and is often done in a few minutes while the baby sleeps.
• Auditory brainstem response. This test uses wires (electrodes) attached with adhesive to the baby's scalp. While the baby sleeps, clicking sounds are made through tiny earphones in the baby's ears. The test measures the brain's activity in response to the sounds. As in EOAE, this test is painless and takes only a few minutes.

If the screening test shows a possible hearing loss, more testing is needed. Not all babies who fail the first hearing test will be deaf or hard of hearing. Other things may cause your baby to fail this early hearing test. These include excess fluid or earwax in your baby's ear or too much noise in the room where your baby was tested. All babies who don't pass the screening test should be checked by a hearing specialist (audiologist) by age 3 months. Treatment for hearing loss should start before the baby is 6 months old, an important time for speech and language development.