The correct occupational hygiene can access noise exposure during pregnancy and can help reduce the negative effects.
Noise is defined as unwanted or undesirable sound that subjectively disrupts or is physiologically or psychologically stressful for an individual. Negative health effects to high noise levels include noise-induced hearing loss (NIHL), and noise-induced stimulation of the sympathetic nervous system and endocrine system resulting in increased production of stress hormones and increased blood pressure and heart rate.
Within an industrial environment, noise may be a higher risk: noise may be more excessive and there may be interaction with other atmospheric contaminants (ototoxicants) to increase hearing loss. In adults, hearing loss is usually the consequence of repeated exposures to noise resulting in a general reduction in hearing between 3000 and 6000 Hertz.
Due to the changing working environment, more women participate in full-time work with many women choosing to work well into the third trimester. The changing workforce makes it imperative to identify occupational risk factors, such as noise, that could passively impact the foetus prior to birth and to evaluate how well current exposure standards protect these vulnerable groups.
The sound environment in the uterus comprises both internally generated noises along with sounds originating from the external environment. Sound transferral and foetal responsiveness within this environment depend on a variety of factors including; gestational age, sound frequency, and attenuation of the environment to external sounds.
Negative birth effects in relation to noise have been studied in various themes. Some studies focus on hearing impairments, some towards gestational outcomes for the child. Most of the current literature focusses on birth weight and prematurity. Yet, discrepancies within the literature have given a broad overview with no conclusive outcome towards the effects of noise on the foetus.
From a recent review of the literature, there are gaps in what is known and inconsistencies within the studies. Studies that indicated negative health outcomes are showing that some or all of the following may be expected:
- low birth weight;
- small for gestational age;
- pre-term birth; and
- hearing loss.
Perception of sound in the womb has also been revised with the improvement of technology, finding that sound attenuation in the womb is highly associated with gestational development and body positioning compared to the environmental noise.
There are defined exposure standards for safe noise levels for both the time weighted average 8-hour day (85 dBA) and for peak noise levels (140 dB(lin) or dB(C) depending upon the jurisdiction you are in).
Currently, the effects of noise on the foetus remain unconfirmed with gaps in the literature and research towards the effect of noise on the unborn foetus remaining, yet, compelling information from the research already published indicates that occupational sound levels above the 8-hour exposure standard are likely to be hazardous to the foetus.
More research is needed to confirm our understanding:
- towards the health impacts of high sound levels during pregnancy;
- the attenuation of sound levels within the amniotic sac and uterine environment; and
- the role of body position towards permeation of sound into the uterus.
However, we believe there is sufficient evidence that where occupational sound levels exceed the exposure standard the exposure must be mitigated without the use of hearing protection devices for pregnant women: it is recommend that pregnant women are removed from noisy workplaces at eighteen weeks gestation, when the foetal auditory system is developed.
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