Hearing loss in babies can range from mild to profound. Mild hearing loss means the baby’s hearing is not normal but they can still hear some sounds. The level of mild hearing loss ranges from 16 to 40 decibels. This means they may have trouble hearing faint or distant speech. Mild hearing loss in babies has various causes that can occur before, during or after birth.
Causes Before Birth
There are several potential causes of mild hearing loss that can occur before a baby is born:
Genetics
Genetics play a role in about 50-60% of childhood hearing loss. There are certain genetic mutations and syndromes that are associated with mild hearing loss, including:
- Connexin 26 mutation – This is the most common cause of mild-moderate genetic hearing loss.
- Pendred syndrome – Caused by a genetic mutation that affects thyroid function and hearing.
- Jervell and Lange-Nielsen syndrome – Associated with heart problems and hearing loss.
- Stickler syndrome – Connective tissue disorder that can cause vision, joint and hearing problems.
If there is a family history of childhood hearing loss, babies have an increased risk of being born with mild hearing impairment.
Ear Malformations
Malformations of the outer ear, middle ear or inner ear structures can disrupt sound transmission and cause mild conductive hearing loss. These include:
- Microtia – Underdeveloped or misshaped outer ear.
- Atresia – Absence of the external ear canal.
- Malformed ossicles – Middle ear bones.
- Enlarged vestibular aqueduct – Inner ear abnormality.
These malformations are often identified on prenatal ultrasound exams.
Maternal Infections
Certain maternal infections during pregnancy may infect the fetus and affect hearing development:
- Cytomegalovirus (CMV) – CMV is the most common infection that causes congenital hearing loss, often mild or moderate in severity.
- Syphilis – The bacterium that causes syphilis can spread to the fetus and damage structures of the ear.
- Rubella – The rubella virus potentially causes sensorineural deafness when contracted by the mother in early pregnancy.
- Toxoplasmosis – This parasitic infection can lead to deafness with other symptoms in newborns.
Screening and treatment of maternal infections reduces the risks of hearing loss.
Complications of Prematurity
Babies born prematurely are at higher risk of having mild hearing impairment. Contributing factors include:
- Underdeveloped auditory system – The structures of the ear may be immature and vulnerable to damage.
- Prolonged neonatal intensive care – Noise exposure, ototoxic medications and infections associated with the NICU environment can harm hearing.
- Low birth weight – This is linked with a slight increase in hearing problems.
The degree of prematurity correlates with the severity of hearing loss.
Causes During Birth
Certain circumstances during the birthing process can also lead to mild hearing impairment in newborns. These include:
Birthing Difficulties
Difficult, long or operative deliveries may negatively impact hearing in babies. Specific risks include:
- Breech positioning – Pressure on the baby’s head in the birth canal.
- Premature separation of the placenta – Reduces oxygen supply.
- Forceps or vacuum extraction – Can mechanically damage ear structures.
- Extended labor – Potential for oxygen deprivation.
- Emergency C-section – Necessary in response to fetal distress.
Jaundice
Jaundice is a common condition in newborns involving a buildup of bilirubin. Mild cases are harmless, but severe untreated jaundice can damage hearing resulting in auditory neuropathy spectrum disorder.
Medications
Certain medications given to women during childbirth may cross the placenta and affect the fetal auditory system. These include:
- Aminoglycoside antibiotics
- Furosemide diuretics
- Nonsteroidal anti-inflammatory drugs (NSAIDS)
Ototoxic drugs should only be given with caution during delivery if absolutely necessary.
Causes After Birth
There are also a variety of causes of acquired mild hearing loss that can occur in babies and young children after birth. These include:
Ear Infections
Recurrent middle ear fluid and infections (otitis media) are a very common cause of mild conductive hearing loss in babies and toddlers. The fluid prevents normal vibration of the eardrum and small bones of the middle ear.
Noise Exposure
Exposure to loud noises can damage the delicate inner ear structures in babies. This is still fairly uncommon but possible sources include:
- Noisy hospital neonatal intensive care units
- Parents listening to loud music or television
- Older siblings playing with noisy toys
Head Trauma
Any head injury or trauma that affects the ear structures can potentially lead to mild sensorineural or conductive hearing loss in babies. Fractures of the temporal bone or damage to the cochlea are possible.
Postnatal Infections
Bacterial meningitis is the most common postnatal infection associated with mild childhood hearing impairment. The bacteria infect the meninges (protective membranes) surrounding the brain and inner ear structures.
Medications
Certain prescription drugs can damage the auditory system in babies and children resulting in ototoxicity and mild hearing problems. These include:
- Aminoglycoside antibiotics
- Cisplatin chemotherapy
- Loop diuretics
- Antimalarial drugs
Congenital CMV
Babies born with congenital cytomegalovirus infection may develop sensorineural hearing loss in the months following birth even if their initial newborn hearing screen was normal.
Diagnosing Mild Hearing Loss
Detecting mild hearing impairment in babies relies on a combination of tests:
Newborn Hearing Screening
Universal newborn hearing screening is recommended for all babies and mandated in many states. Automated auditory brainstem response (ABR) testing and otoacoustic emissions (OAE) testing is used to screen hearing within the first few days after birth.
These automated screens are very effective at detecting moderate, severe or profound hearing loss but less reliable at identifying milder impairment. Babies with risk factors may need additional screening as outpatients.
Diagnostic ABR
If a baby fails automated newborn screening, diagnostic ABR will be performed by an audiologist. This test measures how the auditory nerve and brainstem respond to sound. It is the gold standard for determining the degree of hearing loss.
Other Tests
Other hearing tests that may help diagnose mild hearing loss in babies include:
- Tympanometry – Measures middle ear function.
- Acoustic reflex testing – Evaluates auditory nerve pathways.
- OAE testing – Confirms inner ear responses.
- Behavioral audiometry – Assesses hearing thresholds (once baby is older).
Thorough examination and imaging like CT or MRI scans also helps identify potential anatomical abnormalities contributing to hearing problems.
Effects of Mild Hearing Loss
The effects of mild hearing impairment in babies may be subtle but can still impact development. Possible effects include:
- Delayed speech and language milestones.
- Difficulty localizing to sound sources.
- Trouble understanding soft speech.
- Behavioral and social issues.
- Learning disabilities.
The earlier mild hearing loss is identified and treated, the less impact it will have on the baby’s language skills. Ongoing developmental monitoring is important.
Treatment of Mild Hearing Loss
Treatment options for mild hearing impairment in babies include:
Hearing Aids
Hearing aids are often the first line treatment approach. Custom fitted aids amplify sounds to improve hearing thresholds. Digital hearing aids can be programmed for the baby’s specific degree of loss.
Ear Tubes
Placement of tympanostomy tubes is a common surgery when fluid in the middle ear is contributing to mild conductive hearing loss.
Medications
Medications may be prescribed for underlying conditions leading to hearing problems, such as antibiotics for ear infections or diuretics for fluid.
Surgery
Surgery like cochlear implantation may be an option for severe cases of hearing loss unresponsive to hearing aids. Surgery can also correct some structural abnormalities.
Speech Therapy
Many babies benefit from early speech and language interventions to optimize development.
Auditory Training
Therapy activities that stimulate listening with aided hearing can help babies maximize use of their residual hearing.
Assistive Devices
Other assistive listening devices like FM systems may supplement hearing aids in group settings once the baby is older.
Monitoring
Ongoing hearing tests are important to monitor status and update interventions accordingly.
Prevention of Mild Hearing Loss
While not all causes can necessarily be prevented, some key recommendations help reduce the risk of mild hearing impairment in babies:
- Prompt prenatal care and infection screening
- Careful fetal monitoring and proper management of at-risk pregnancies
- Follow safe labor practices and NICU noise policies
- Early treatment of newborn jaundice
- Judicious use of ototoxic medications
- Minimize noise exposure after birth
- Breastfeed and follow vaccination schedules to reduce ear infections
- Universal newborn hearing screening
- Refer babies with risk factors for audiological monitoring
Conclusion
Mild hearing loss has a variety of possible causes in babies related to genetics, birth defects, complications of pregnancy and delivery, infections, noise, trauma and medications. While often undiagnosed at birth, even mild impairment can delay language development. However, early identification and appropriate interventions help optimize outcomes. Ongoing research aims to better understand the complex causes of hearing loss and refine preventative strategies and treatments.