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      Maternal Occupational Exposure to Noise during Pregnancy and Hearing Dysfunction in Children: A Nationwide Prospective Cohort Study in Sweden

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          Abstract

          Background:

          Many women of childbearing age are occupationally active, which leads to a large number of pregnancies potentially exposed to occupational exposures. Occupational noise has been identified as a risk factor for hearing impairment in adults. However, very few studies have assessed the effect of occupational noise on the fetus.

          Objectives:

          The aim of this study was to investigate whether occupational exposure to noise during pregnancy is associated with hearing dysfunction in children.

          Methods:

          This population based cohort study included 1,422,333 single births in Sweden 1986–2008. Data on mothers’ occupation, smoking habits, age, ethnicity, body mass index, leave of absence, and socioeconomic factors were obtained from interviews performed by prenatal care unit staff at approximately 10 weeks of gestation and from national registers. Occupational noise exposure was classified by a job–exposure-matrix as < 75, 75–84, or ≥ 85 dBLAeq,8h. Diagnosed cases of hearing dysfunction (ICD-10 codes H90.3-7, 91.0, 91.2-3, 91.8, 93.1-2) were identified from a register of specialized medical care. Cox proportional hazards models were used to estimate associations.

          Results:

          In the full sample, containing a mixture of part-time and full-time workers during pregnancy, the adjusted HR for hearing dysfunction associated with maternal occupational noise exposure ≥ 85 vs. < 75 dBLAeq,8h was 1.27 (95% CI: 0.99, 1.64; 60 exposed cases). When restricted to children whose mothers worked full-time and had < 20 days leave of absence during pregnancy, the corresponding HR was 1.82 (95% CI: 1.08, 3.08; 14 exposed cases).

          Conclusions:

          This study showed an association between occupational noise exposure during pregnancy and hearing dysfunction in children. In view of mechanistic evidence and earlier indicative epidemiological and experimental findings, the results support that pregnant women should not be exposed to high levels of noise at work.

          Citation:

          Selander J, Albin M, Rosenhall U, Rylander L, Lewné M, Gustavsson P. 2016. Maternal occupational exposure to noise during pregnancy and hearing dysfunction in children: a nationwide prospective cohort study in Sweden. Environ Health Perspect 124:855–860; http://dx.doi.org/10.1289/ehp.1509874

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          Most cited references33

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          Math1 regulates development of the sensory epithelium in the mammalian cochlea.

          The transcription factor Math1 (encoded by the gene Atoh1, also called Math1) is required for the formation of mechanosensory hair cells in the inner ear; however, its specific molecular role is unknown. Here we show that absence of Math1 in mice results in a complete disruption of formation of the sensory epithelium of the cochlea, including the development of both hair cells and associated supporting cells. In addition, ectopic expression of Math1 in nonsensory regions of the cochlea is sufficient to induce the formation of sensory clusters that contain both hair cells and supporting cells. The formation of these clusters is dependent on inhibitory interactions mediated, most probably, through the Notch pathway, and on inductive interactions that recruit cells to develop as supporting cells through a pathway independent of Math1. These results show that Math1 functions in the developing cochlea to initiate both inductive and inhibitory signals that regulate the overall formation of the sensory epithelia.
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            Development of fetal hearing.

            Previous research has revealed that the human fetus responds to sound, but to date there has been little systematic investigation of the development of fetal hearing. The development of fetal behavioural responsiveness to pure tone auditory stimuli (100 Hz, 250 Hz, 500 Hz, 1000 Hz, and 3000 Hz) was examined from 19 to 35 weeks of gestational age. Stimuli were presented by a loudspeaker placed on the maternal abdomen and the fetus's response, a movement, recorded by ultrasound. The fetus responded first to the 500 Hz tone, where the first response was observed at 19 weeks of gestational age. The range of frequencies responded to expanded first downwards to lower frequencies, 100 Hz and 250 Hz, and then upwards to higher frequencies, 1000 Hz and 3000 Hz. At 27 weeks of gestational age, 96% of fetuses responded to the 250 Hz and 500 Hz tones but none responded to the 1000 Hz and 3000 Hz tones. Responsiveness to 1000 Hz and 3000 Hz tones was observed in all fetuses at 33 and 35 weeks of gestational age, respectively. For all frequencies there was a large decrease (20-30 dB) in the intensity level required to elicit a response as the fetus matured. The observed pattern of behavioural responsiveness reflects underlying maturation of the auditory system. The sensitivity of the fetus to sounds in the low frequency range may promote language acquisition and result in increased susceptibility to auditory system damage arising from exposure to intense low frequency sounds.
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              • Abstract: found
              • Article: not found

              Fetal exposures to sound and vibroacoustic stimulation.

              Sounds in the environment of a pregnant woman penetrate the tissues and fluids surrounding the fetal head and stimulate the inner ear through a bone conduction route. The sounds available to the fetus are dominated by low-frequency energy, whereas energy above 0.5 kHz is attenuated by 40 to 50 dB. The fetus easily detects vowels, whereas consonants, which are higher in frequency and less intense than vowels, are largely unavailable. Rhythmic patterns of music are probably detected, but overtones are missing. A newborn human shows preference for his/her mother's voice and to musical pieces to which he/she was previously exposed, indicating a capacity to learn while in utero. Intense, sustained noises or impulses produce changes in the hearing of the fetus and damage inner and outer hair cells within the cochlea. The damage occurs in the region of the inner ear that is stimulated by low-frequency sound energy.
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                Author and article information

                Journal
                Environ Health Perspect
                Environ. Health Perspect
                EHP
                Environmental Health Perspectives
                National Institute of Environmental Health Sciences
                0091-6765
                1552-9924
                8 December 2015
                June 2016
                : 124
                : 6
                : 855-860
                Affiliations
                [1 ]Institute of Environmental Medicine, Unit of Occupational Medicine, Karolinska Institutet, Stockholm, Sweden
                [2 ]Centre for Occupational and Environmental Medicine at Stockholm County Council, Stockholm, Sweden
                [3 ]Division of Occupational and Environmental Medicine, Lund University, Lund, Sweden
                [4 ]Department of Audiology and Neurotology, Karolinska University Hospital, Stockholm, Sweden
                Author notes
                []Address correspondence to J. Selander, Institute of Environmental Medicine, Unit of Occupational Medicine, Karolinska Institutet, Solnavägen 4, 113 65 Stockholm, Sweden. Telephone: 0046-8-52480029, 0046-73-9795476. E-mail: Jenny.Selander@ 123456ki.se
                Article
                ehp.1509874
                10.1289/ehp.1509874
                4892921
                26649754
                65c5edbf-23ab-4720-aef3-d07afb1f31a4

                Publication of EHP lies in the public domain and is therefore without copyright. All text from EHP may be reprinted freely. Use of materials published in EHP should be acknowledged (for example, “Reproduced with permission from Environmental Health Perspectives”); pertinent reference information should be provided for the article from which the material was reproduced. Articles from EHP, especially the News section, may contain photographs or illustrations copyrighted by other commercial organizations or individuals that may not be used without obtaining prior approval from the holder of the copyright.

                History
                : 24 February 2015
                : 23 November 2015
                Categories
                Children's Health

                Public health
                Public health

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