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Risk Factors During Pregnancy

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In children with severe hearing loss, a family history of hearing loss is the most common factor [73].

1.5.1.2 Risk factors during pregnancy


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1.5.1.2.1 Infections during pregnancy


Risk Factors During Pregnancy

Mothers with certain infections such as Rubella and Syphilis during pregnancy may cause hearing loss or deafness in their children [128]. A case-control study in Bangladesh showed that 74% of children with hearing loss had rubella antibodies (IgG), while only 18% of children without hearing loss had this antibody. The study also showed that 67% of mothers of children with hearing loss had this antibody, while only 14% of mothers of children with normal hearing had IgG. Thus, there is a correlation between Rubella and hearing loss in children in this country [96]. A case-control study in Denmark (1980) with children aged 0-4 years with congenital sensorineural hearing loss found that 60% of children with hearing loss had rubella antibodies in their blood, while only 23.0% of the control group had this antibody. Studies have shown that rubella infection during pregnancy plays an important role in causing hearing loss in infants and young children [93].

1.5.1.2.2 Using drugs during pregnancy


Use of certain toxic drugs such as aminoglycosides, cytotoxic drugs, antimalarial drugs, and diuretics during pregnancy carries a risk of congenital hearing loss [128].

1.5.1.3 Risk factors during birth


1.5.1.3.1 Premature birth, low birth weight


The association between premature birth, low birth weight (<1500g) and hearing loss has been reported in many studies worldwide. However, the underlying mechanism of this association is still not well understood. Although prematurity and low birth weight alone do not significantly affect hearing loss,

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However, low birth weight infants often have many other risk factors combined (such as jaundice with increased free bilirubin, respiratory failure requiring mechanical ventilation, oxygen therapy, intraventricular hemorrhage, sepsis), thereby increasing the possibility of hearing loss in these infants.

A Norwegian cohort study from 1967 to 1993 involving 1,548,429 newborns found a hearing loss prevalence of 11/10,000 children. The prevalence decreased from 60/10,000 in children with a birth weight <1,500 g to 6/10,000 in those with a birth weight >4,499 g. The study also found that birth weight was a protective factor for hearing loss in newborns. Compared with children born with a birth weight of 3,000 g to 3,499 g, children born with a birth weight <1,500 g had a 7.55-fold higher risk of hearing loss (95% CI: 4.81-11.87). Children born with a high birth weight of 4,499 g or more are twice as likely to have hearing loss than children born with a birth weight of 3,000 g - 3,499 g [91]. A 10-year cohort study of children aged 3-10 years in the United States showed that the rate of hearing loss increased inversely with the birth weight of the children. The rate of hearing loss was higher in children with a lower birth weight. The study also proposed criteria for screening for hearing loss in children with a birth weight of 2,500 g - 29,999 g and 15,000 g - 2,499 g [114].

Similar to the epidemiological studies mentioned above, many other studies have also found a link between hearing loss and birth weight. [57], [119]. Research in our country in recent years has also shown that premature babies are at higher risk of hearing loss than full-term babies. Research at the Central Maternity Hospital showed that premature babies are at 9.71 times higher risk of hearing loss than full-term babies [37]. However, research at the Central Children's Hospital on premature babies did not find any link between hearing loss and this risk factor [12].

1.5.1.3.2 Lack of Oxygen


Hypoxia is closely associated with hearing loss. Cochlear function is normal when there is adequate oxygenation and perfusion. Newborns


Hypoxia or asphyxia affects the cochlear ganglion cells first. More severe hypoxia causes destruction of the cochlea, especially the outer hair cells and stria vascularis. However, there is no established threshold for the degree of hypoxia that affects hearing. Furthermore, newborns with respiratory distress are often ventilated and/or have alkalosis, which further reduces oxygenation and blood flow to the cochlea and auditory nerve pathways, leading to hearing loss.

A study in the US showed that among 1,279 children receiving intensive treatment, 3.1% had permanent hearing loss and 1.9% had severe/very severe hearing loss. Prolonged oxygen therapy intervention was an important risk factor for hearing loss in children requiring intensive treatment, OR: 4.61 (95%CI: 1.98-10.71) [97]. A study in our country in 2011 showed that oxygen therapy for more than 7 days was a risk factor for hearing loss in high-risk children treated at the Intensive Care Unit of the National Children's Hospital [12].

1.5.1.3.3 Postpartum jaundice


Increased free bilirubin can selectively damage the auditory brainstem nuclei and can also destroy the auditory nerve and cochlear ganglion cells by causing intracellular calcium stasis in neurons. The organ of Corti and the thalamocortical auditory nerve pathway are usually spared. Clinically, retrocochlear hearing loss is common. In this case, OAE measurements may be normal but AABR may be abnormal. Severe neonatal jaundice can cause auditory nerve damage, leading to hearing loss in children [128]. Cochlear sound measurements in 128 infants with neonatal jaundice in Malaysia showed that 22% had hearing loss. Logistic regression analysis showed that jaundice was a factor associated with hearing loss in this group of infants [58].


1.5.2. Causes of acquisition


1.5.2.1 Children with infections


1.5.2.1.1 Meningitis


Meningitis is an important factor causing hearing loss in children [128]. It is also the most common cause of acquired sensorineural hearing loss [71]. About 10% of children have varying degrees of hearing loss after meningitis. Hearing loss associated with meningitis is a complex mechanism, during which inflammation causes brain and meningeal edema, reducing oxygen to nerve cells. This causes irreversible damage to nerve cells. Children with meningitis are at the highest risk of deafness. Children with purulent meningitis may become deaf a few days after the illness [71].

A cohort study of 432 children with VMN in the UK found that 59 (13.7%) had hearing loss, of which 46 (78%) had permanent sensorineural hearing loss, the remainder had sensorineural or fluctuating hearing loss [131].

1.5.2.1.2 Chronic otitis media


The ossicles in the middle ear have the function of transmitting and increasing sound wave energy from the outer ear to the inner ear. When suffering from VTG, fluid or pus accumulates in the tympanic cavity, hindering the vibration of the ossicular chain, causing sound wave energy to be lost, thereby reducing hearing. In this case, it is called conductive hearing loss and is usually mild to moderate. In general, deafness due to VTG, if treated properly and promptly, will recover completely. On the contrary, if not treated, it can turn into mixed deafness or sensorineural deafness and cannot be recovered.

WHO indicates that approximately 90% of otitis media cases occur in countries in the Southeast Asia, Western Pacific, and African regions [129]. This disease can cause otitis media with effusion in approximately 65 to 330 million children.


people worldwide, thus contributing to global hearing loss. Epidemiological studies have shown that chronic otitis media (CotIT) is an important cause of hearing loss and deafness in children.

1.5.2.2 History of drug use in children


1.5.2.2.1 Antibiotics


Antibiotics are good options for treating bacterial infections, but they can affect the cochlea and vestibular system. Antibiotics that are most likely to cause hearing loss include streptomycin, gentamicin, and tobramycin. These agents can cause hearing loss by causing death of hair cells. They disrupt the transmission of electrical signals at nerve synapses or destroy nerve and cochlear cells [120]. Recent studies are focusing on minimizing the harmful effects of this group of drugs on hair cells [70].

In general, drug toxicity is often related to the duration of treatment, the maximum and minimum drug concentrations in the blood, a history of using aminoglycoside antibiotics, combining the drug with Vancomycin or the time of taking diuretics. Therefore, the maximum and minimum drug concentrations in the blood are often monitored during treatment. Using serial audiometric testing is a very good measure to monitor and detect early drug toxicity. In 1994, the American Speech-Language-Audiology Association issued guidelines for audiometric testing before starting, within the first 72 hours of using aminoglycosides and then weekly monitoring. However, this guideline is not feasible in clinical practice.

One solution is to use a single daily dose of aminoglycoside, which is more convenient and less expensive. Two randomized controlled clinical trials comparing once-daily and multiple daily doses of gentamicin in septic neonates found that single-dose administration was safe and effective. However,

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However, some authors are still concerned about the toxicity of the drug when the peak concentration of the drug will be higher.

Research in the United States shows that medical poisoning is the leading risk factor for hearing loss in high-risk infants requiring intensive care. The study found that 44.4% of children with hearing loss had a history of exposure to toxic drugs [119].

1.5.2.3 Injury


Head and ear injuries can cause temporary or permanent hearing loss. Head injuries can damage the brain, meninges, perforate the tympanic membrane, and affect the structures of the inner ear, which can lead to hearing loss [44]. However, the effects of hearing loss due to head injury are often detected late. A cohort study of patients with head injuries from motor vehicle accidents in South Africa showed that, on average, it took 8.2 years before hearing loss was assessed in these subjects [54].

1.5.2.4 Noise


Noise is described as an unwanted sound that can have harmful effects on human health and life. In terms of physics, sound propagates in the form of waves in air or other mechanical medium, with the main characteristics being intensity and frequency [43].

In the past, infections (ear discharge) were the biggest culprits causing hearing loss in children. However, as the rate of infections is decreasing, noise-induced hearing loss is becoming the leading cause of hearing loss worldwide [124]. Sounds louder than 85dB can cause permanent hearing loss. High-intensity sounds can affect the receptors in the cochlea and vestibule and the blood supply to the cochlea. Therefore, if exposed to loud noise for a long time, its effects on hearing ability will occur. Hearing loss due to many different causes and other risk factors such as aminoglycoside antibiotics combined

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Noise intensity above 115 dB is considered dangerous for children because it can cause deafness and hearing loss even after only one exposure for 3 to 15 minutes. This type of noise can be found in large dance halls, near electronic music speakers playing at high power, truck horns, bells, and gongs. Sound intensity above 100 dB causes obvious harm after exposure for a few minutes to a few tens of minutes on a few days (depending on age). This noise can be found in train stations, bustling shopping areas, radios, and family music systems played at high levels. In children, noise intensity above 80 dB is harmful because it makes sleep not deep, respiratory and digestive activities are easily disturbed, and affects thinking and learning. If having to live regularly in such a noisy place, young children may suffer from hearing loss.

1.5.2.5 Other factors


Other factors that can cause hearing loss in children include earwax or foreign objects stuck in the ear. These conditions can cause hearing loss, but once the foreign object or earwax is removed, the hearing loss will go away.

1.5.2.6 Hearing loss of unknown cause


Hearing loss of unknown cause accounts for a large proportion of total hearing loss. In the United States, reports indicate that approximately 54% of hearing loss cases are of unknown cause (2004-2005). Reports from 2006-2007 indicate that up to 57% of hearing loss and deafness cases have no identifiable cause [55].

1.6. Effects of hearing loss


One of the effects of hearing loss on human functioning is the ability to communicate with others. Children with severe hearing loss and deafness often do not develop language and speech like other children [72]. Hearing loss and ear diseases such as otitis media also have a serious impact on children's learning ability [105]. Studies on hearing loss in primary school children


Studies have shown a correlation between hearing loss and poor academic performance in these children [98].

People with hearing loss are often not able to participate and integrate freely into social activities. Sometimes they are excluded from community activities due to the perception that hearing loss or deafness cannot do the same things as other people. This can lead to psychological and social effects for people with this problem.

1.7. Hearing loss interventions


Currently, there are many intervention solutions for people with hearing loss. Depending on the actual conditions of the hearing loss subjects, appropriate hearing loss intervention solutions will be applied, including the following solutions [47]:

- Hearing aids


- Language recovery


1.7.1. Hearing aids


Hearing aids are devices that can help people with hearing loss perform everyday communication functions. Hearing aids may or may not be used with other assistive listening devices or technologies or cochlear implants to enhance hearing in people with hearing loss. Hearing aids are divided into two main types: Hearing aids and Cochlear implants [47].‌

1.7.1.1 Listening device


Hearing aids are small electronic devices worn behind the ear that make sounds louder so that deaf people can hear and participate in social activities. Hearing aids can help people hear in both quiet and noisy environments.

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