Risks to pregnant women and unborn babies from high noise
A client recently asked me if pregnant women are OK to work in an environment with a noise level which is considered ‘high’, so over 85 dB(A), or whether the noise can cause risk to either the pregnancy or foetus.
For an overall answer I would say ‘check with their medical professional as I am not a medical professional’, but it was an interesting question which I looked further into.
There seems to be a lot of dubious opinion on various websites about this which are presented as fact, no surprises there as the whole baby thing seems to be drowning in fervent but unsupported opinion. Where I have made a statement I have included links to the sources of the information I have quoted, so anyone can refer back to the original source of the data. I have limited sources to ‘reputable’ sites rather than opinion pieces.
Risks seem to focus on two things:
Hearing damage as the baby develops
An impact on birth weight from high noise
What noise level is a risk to an unborn baby?
Firstly, it seems that unborn babies can indeed have their hearing damaged by high noise which makes sense - they hear just the same way the mother does and the cochlea in the ear develops really early on. But, the noise within the womb is attenuated by the woman’s body so the noise a foetus receives is not the same as the noise the mother is hearing. Studies show the womb is 25 to 35dB quieter than outside the body. (Link).
In trying to pin down a source for what noise level starts to have a risk, the one thing which became clear is that there seems to be some considerable variations in what is considered a dangerous noise level for a prospective mother.
One source which is a widely acknowledged source of expertise, even for those of us outside Americaland, is the US Centres for Disease Control who say pregnant women should avoid regular consistent noise of 115 dB(A) or over to avoid hearing damage in the baby. (Link). That’s regular and consistent - so repeatedly and for prolonged times.
Another study meanwhile, available on Science Direct (Link) and quoting a Swedish study sets 85 dB(A) as the maximum sound level for occupational noise, not due to hearing in this case but due to the impact on birth weight.
Some other studies seem to separate from reality a little. For example the National Library of Medicine references a study (link) saying noise should not exceed 50 to 55dB. That’s quieter than an office, quieter than watching TV at home, and frankly completely unrealistic for life.
It is worth noting that the mother’s heart is reported to be about 90 dB(A) in the womb (Link) which means that itself is louder than some of those lower values.
The 115 dB(A) figure seems to be the most widely referenced and I have also seen that quoted by bodies such as the National Institute for Occupational Safety and Health. For possible hearing damage from high noise to an unborn baby therefore, that is the one which seems to jump out as a good figure. Just to repeat, that is an average exposure by the way, over a working day, not a one-off instance of it.
Is there a proven link between noise and hearing damage to an unborn baby?
This is an interesting question as it seems the answer is ‘nobody is entirely sure’. It is one thing saying ‘this level of noise is safe / dangerous’, but is there a proven link between high noise and harmful effects on an unborn baby?
In a Guardian Q&A article a doctor stated there is no proven link between instances of high noise and hearing damage to an unborn baby. (Link)
One of the scientific links above (also here) contains the phrase “no reports with adequate controls [meaning checks to make sure the data is right] have demonstrated in utero hearing loss because of external noise”. It also says “pregnant women should not unnecessarily be removed from the work force”.
The Science Direct article says continual exposure at work to levels of 85 dB(A) or over can inhibit foetal growth, (not ‘will’, ‘can’), but it then also says further studies are needed.
So it seems to be rather uncertain as to whether high noise is indeed a confirmed problem. Common sense would seem to say chances are it may be, but that dangerous noise levels must be nearer the 115 dB(A) quoted rather than the much lower 85 dB(A). If 85 dB(A) did indeed cause a problem, every pregnant woman who gets the Tube to work and back will have been giving birth to deaf or small children since the Tube was invented.
Summary on noise impact on an unborn baby
So, it seems there is a possibility that noise could maybe damage hearing, although not conclusively proven.
And that the ‘dangerous’ continual noise level seems to be 115 dBI(A).
That average of 115 dB(A) is well above the vast majority of workplaces, I don’t think I’ve ever seen one with that as an average.
Noise may impact birth weight and the study for that seems to say 85 dB(A) as the level. But that doesn’t seem to be widely repeated so I am reluctant to take it as an absolute fact.
85 dB(A) is a very common noise level at work and also in non-work environments.
If worried then don’t rely on websites, even this one, as the Internet is not a good source for critical information. Go and speak to a medical professional.
As I opened with I am not an expert on this but am curious so this is comment only.
