Hearing Loss within the Womb

November 3, 2016

Great Expectations

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Hearing development and hearing loss within the womb are topics which have not been thoroughly studied but they are being addressed more in the last several years which builds our knowledge base.

Preparing to welcome a child into the world is an exciting and busy time full of planning, educating oneself on what to expect, and a diverse range of emotions. Expectant parents are committed and eager to minimize any and all potential threats to their unborn children including the possibility of hearing impairment.

The reality is that in many cases congenital- and infant hearing loss cannot be prevented and often it is difficult to determine the exact cause. It is of utmost importance that we steer clear of drawing ill-informed conclusions or placing harmful blame on those made vulnerable by experiencing the birth of a child with hearing loss.

Let us examine what we do know and what we don’t know so we can strive to make our individual choices with confidence, empowered with knowledge.

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The development of Baby’s hearing in the womb

The Unborn Infant’s brain develops the capacity to hear as the inner ear structures develop in vitro between 23-25 weeks of age.

Research completed by the PNAS (Proceedings of the National Academy of Sciences) showed that while in gestation, infants can begin to distinguish the differences between syllables and male and female voices at 28 weeks of age. These findings are exciting for those who wish to communicate with their child before it is born. They also shed light on why a newborn reacts to the voice of its biological mother nearly immediately after birth due to the child literally recognizing it.

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Genetic Hearing Loss

Seventy five percent of infants who are born with hearing impairment are thought to be affected by genetic factors. These factors might be well-known due to family histories or be completely unexpected. At this point there is no comprehensive genetic screening which could alert parents to hearing loss before birth. If you are aware of an increased risk of hearing impairment in your family, you and/or your partner may want to receive counselling before the birth to address the possibility regarding the increased chance of a child born with hearing loss.

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Non-genetic factors of hearing loss

The remaining twenty five percent of those born with hearing loss have a non-genetic factor which may have affected their condition and can sometimes be identified. The most common of these are illness or trauma before or during birth.

Low Birth Weight - has been flagged as a risk factor for hearing loss; with experts saying that those born weighing less than 1500 grams (about 3.3lbs) are at an increased risk for hearing loss.

Viral infections -Syphilis, Toxoplasmosis, Measles, & Herpes are four common infections which may impact hearing loss. It should be noted that many infants are exposed to viral infections without any ill effects on their hearing whatsoever!

Illness – Severe jaundice which requires blood transfusion may negatively affect hearing ability in infants. Excessive amounts of Bilirubin (the yellow orange colour of bile pigment, visible in those with jaundice) can cause damage to delicate nerves needed for hearing.

Medications – Medicine which is known and recognized to be damaging to hearing is known as “Ototoxic medicine”. There are times when infection or complications from birth may necessitate these medications being used in spite of the risk. Aminoglycoside antibiotics are known as ototoxic and include gentamycin, kanamycin, streptomycin, and tobramycin. The risk is increased if multiple rounds of antibiotics are used and if they are used in conjunction with other medications.

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Can I damage my baby’s hearing in the womb?

There is not one definite answer to this question. Here are the outlines of what we know about sound in the womb.

- Sudden loud noises may startle a baby and cause increased activity for a short while after the sound. However, a study done in the Netherlands and published in The Lancet showed that while foetus’s first reacted to a new sound, they became ‘used’ to or habituated to sound in the womb, showing decreased sensitivity when exposed to the sound repeatedly.

- Amniotic fluid and the uterine wall acts as a buffer zone between the womb and the outside world of sound for your baby. This fluid fills the baby’s ears and works to muffle high frequency sounds.

- Sounds in the 150 decibels and up range have the potential to negatively affect hearing in the womb as does continuous noise over 90-100 decibels. It ought to be noted that these are the same volume levels which can and do cause preventable hearing loss in children and adults.

- It has also been highly recommended that you do not place earphones or speakers directly onto your skin in the pursuit of playing your unborn child some music as this may result in damage to the featus’ hearing capabilities.

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What can I do to protect my baby’s hearing before it is born?

To best care for your baby’s hearing, take good care of yourself, emotionally, psychologically and physically and receive regular prenatal health check-ups!

Feeling the best you possibly can and being aware of your body’s special needs and challenges during pregnancy will contribute toward helping you to create the most nurturing environment for your baby in the womb.

If you have questions or concerns about an activity’s impact on you and your baby, seek professional advice from a qualified healthcare provider.

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Importance of infant hearing screening tests

Having a newborn’s hearing screened is an important way to determine if your child has been born with hearing impairment. The test only takes a few minutes and is normally performed by an audiologist in hospital. Babies can be tested as soon as 12 hours after birth.

An Otoacoustic Emission Test (OAE) is a subjective screening test which records responses (vibrations) from the inner ear (cochlea) by placing a small probe in the baby’s ear canal.  Soft, high frequency sounds are then presented through the probe and the inner ear responds by sending vibrations back in to the ear canal.  The microphone in the probe measures these vibrations and a result is obtained.  The test is done while the baby is sleeping or feeding and is completely painless. (OAE information supplied courtesy of the Gauteng Baby Hearing Project) Early detection is absolutely vital to ensure early intervention, whether it be for a hearing aid, cochlear implant or bone anchored hearing implant.

The team at Southern ENT has experience and can be trusted for a lifetime of sidekick support in the fight against hearing loss!

For any information or advice, please call our offices on 011 667 6243

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