What must women avoid during pregnancy?

Pregnancy can be an anxious time full of contradictory advice: exercise is healthy, but don't overdo it. It's safe to use your mobile phone, but perhaps don't make too many calls. Don't drink too much caffeine, but the occasional cup of tea probably won't do any harm. No hot baths or hot tubs, although swimming is probably good for you. Eat a balanced diet… but no goat's cheese, shellfish, runny eggs, pâté or rare meat, and we're not completely sure about ham, tuna and salami.

Contradictory advice for pregnant women often sounds like "out of the frying pan, into the fire".
Image credit: waferboard

It can leave you feeling as though you might be better off locking yourself in a padded room for the duration with nothing but bread, water and pregnancy vitamins. This isn't helped by newspaper headlines such as the ones following the recent publication, by the Royal College of Obstetricians and Gynaecologists (RCOG), of a scientific impact paper on chemical exposures during pregnancy. The headlines ran the full gamut from “Pregnant women warned over household product chemicals” to the flat-out hysterical “Pregnant women told to avoid painting the nursery, buying new furniture or going near non-stick FRYING PANS as they may expose their unborn baby to dangerous chemicals”.

However, perhaps the most striking thing about the original paper is its title: “Chemical Exposures During Pregnancy: Dealing with Potential, but Unproven, Risks to Child Health”. In other words, they've compiled a long list of things that might be harmful, but which they're not really sure about. Do a little web searching for "things to avoid in pregnancy" and you will quickly find that many, many people have already written similar lists. However, this paper wasn't written by just anyone. It was written by the Royal College of Obstetricians and Gynaecologists, and unlike many commentators they did take the trouble to reference their comments thoroughly, reviewing the literature and assessing what evidence they found. The report examined a number of issues; let's look at them in a bit more detail.

Firstly everyone, pregnant woman or otherwise, is exposed to certain chemicals found in everyday products, such as bisphenol A (BPA) and phthalate esters. It's very difficult to identify the effect of such exposures, because these substances are so widespread that there's no unexposed control group with which to compare them.

Living under a rock - not recommended by TWDK.
Image credit: Frank_am_Main

The fact that these chemicals are so widespread is significant. There are hundreds of thousands of healthy births in the UK every year. Every one of those women will have been exposed to common household chemicals (unless they live under a rock in a cave somewhere, in which case they probably have other things to worry about) and yet we seem to have a lot of healthy babies. If these, very widespread, substances do cause significant harm, why aren't we seeing more problems?

Ok, but perhaps they do cause problems, we're just not seeing them at birth. What about more subtle and long-term issues? What about rising cases of allergies, for example? There are, of course, various theories to explain that – such as the hygiene hypothesis and changes in the foods we're eating. But is it possible that environmental chemicals might be exacerbating the problem? It's a question that is, as yet, unanswered, and it's a tricky one to untangle.

Speaking of food, oily fish is an excellent source of omega-3 fatty acids - in particular the long-chain ones EPA and DHA. DHA is considered crucial for healthy brain development and function, and is the subject of quite a bit of research. Although the jury is still somewhat out on the health benefits of supplementation (with, for example, fish oil capsules) the NHS is convinced enough to say that “a healthy diet should include at least two portions of fish a week, including one of oily fish”. And yet, because of the small risk of environmental contaminants building up in fish, as the RCOG report states: “current UK guidelines advise pregnant women to reduce or eliminate their consumption of oily fish during pregnancy”.

It's an interesting question: which is worse? Does the risk of environmental contaminants outweigh the risk of being deficient in essential fatty acids at a time when you need them more than ever? A pregnant woman is, after all, growing at least one whole new brain from scratch, and she needs essential fatty acids to do that. This dilemma really needs addressing, because at the moment mothers are being pulled in two different directions.

Things We Don't Know seeks to explain the questions that scientists are currently working on.

So is it being addressed by researchers? It's difficult to be sure; perhaps there is a group working on this very question right now. Actually, this is one of the aims of Things We Don't Know: to explain the questions that scientists are currently working on and to allow users to subscribe to updates on any they find interesting. The intention is to give you a chance to find out more about scientific areas in which you might be interested without having to wait for a newspaper to report the story. And for those in academia, it might just save those hours and hours of trawling through journals looking for a title that might be half-way relevant. Instead you simply subscribe to updates on, say, work on essential fatty acids, and receive a notification every time there's a newly-published paper. It's a brilliantly simple idea that will allow anyone that's interested to keep up to date with the latest research in whatever topic interests them.

But back to the dangers to which pregnant mothers may, or perhaps may not, be exposed. BPA and phthalates are endocrine-disruptors, which means they are chemicals with the potential to interfere with hormone systems in the body. They both turn up in plastics and a number of other common household substances, and they've been tested for safety many times. The problem is that the safety of chemical exposure is, at the moment, still often expressed in terms of lethal doses. In reality of course, unless they happen to work in the chemical industry, few women come into contact with anywhere near the levels needed for a lethal dose. But they do come into contact with mixtures of a number of different chemicals at low levels. What we don't have, at the moment, are ways to accurately assess the dangers of these chemical mixtures.

Of course there are common-sense steps anyone can take to reduce their exposure, such as eating fresh food rather than processed, minimising the use of personal care products such as cosmetics and fragrances and avoiding things like paint fumes. All very sensible, particularly when pregnant.

But with all this talk of 'chemicals', is there another danger? There seems all too often to be an assumption that the labels 'natural' or 'herbal' mean 'safe'. More than once I've heard someone say that they "don't use chemicals", seemingly under the impression that the bottles of 'organic' or 'eco' products that they do use are somehow chemical-free. Of course this is impossible. Quite apart from the fact that water is technically a chemical, a quick look at the ingredients in a well-known brand of 'eco' cleaning products will show you that they contain sodium lauryl sulfate (SLS), for example, just as other detergent-based cleaning products do. Many a study has shown SLS is pretty safe, but some people do have sensitivities to it. So it's genuinely possible that sloshing around an eco cleaning product, on the assumption that it's completely harmless, might cause problems for certain individuals.

Smoking during pregnancy can harm your baby.
Image credit: Military Health

Likewise for products claiming to only contain plant-based ingredients. Coming from a plant hardly guarantees anything as safe. After all, tobacco, and therefore nicotine, comes from plants, and that's a deadly nerve toxin. Of course we know that women shouldn't smoke during pregnancy, but what about herbal remedies? What about herbal teas? Many women probably think that herbal teas are much safer than regular black tea (which contains caffeine) during pregnancy, but is this truly the case?

Herbal medicines in general are largely unregulated. Sometimes ingredients have various different names and aren't listed particularly clearly, and some may be safe used one way but not another. Aloe vera, for example is generally considered safe to use on the skin, but is not safe to ingest while pregnant. Still, many of the risks from herbal ingredients are fairly well documented, certainly when compared to the far less well-understood risks of exposure to small amounts of chemicals such as BPA and phthalates in the environment, and yet it seems to me that women may be worrying a little too much about the latter whilst being largely unaware of the former.

In fact, I am left with a question: what is the relative risk of these environmental chemical exposures compared to, say, the real biggies of smoking and drinking (large amounts of) alcohol? Why do I pick those? Well, because we know they're definitely damaging. Women that smoke in pregnancy, for example, have double the risk of developing problems with the placenta. We have no such numbers for exposure to everyday chemicals such as those found in food packaging.

Could, for example, a study be carried out in which a group of women are asked to minimise their exposure as much as possible (by following steps like the ones I mentioned earlier), so that their outcomes could be compared to a group that carried on as normal? Obviously the second group wouldn't be a perfect control because eliminating every single exposure to such chemicals is virtually impossible, but it would still be interesting to see if there was any significant difference.

I can't help feeling this would be really worthwhile research. It would be so much better if, instead of talking about “potential, but unproven” risks, we had some hard numbers to fall back on. The facility to support work you'd like to see undertaken is actually another aim of Things We Don't Know. In the future the main TWDK site will allow you to support crowdfunding of research, giving you a genuine opportunity to have a say in the questions you'd like to see answered.

By crowdfunding science, TWDK will enable the public to choose the questions scientists focus on.
Image credit: Rocio Lara

Relative risk is such an important issue. The authors of the RCOG paper make the comment, “It is unlikely that any of these [environmental chemical] exposures are truly harmful for most babies”. Funnily enough though, this wasn't repeated very often, with most commentators preferring to focus on the terrifying dangers of non-stick cooking utensils. The trouble with this sort of reporting is that women might be left with the idea that everything is just as bad as everything else, and so there's no point in giving up alcohol or stopping smoking, because we're 'surrounded' by toxins anyway. Let's have some figures, so that we can properly judge which things are worth giving up and which things simply aren't worth getting stressed about. Let's not forget that stress is also unhealthy - pregnant women really cannot win!

This guest post is by Dr Kat Day. Kat obtained a PhD in Chemistry from the University of Nottingham in 2000, but these days is more usually found in the school laboratory, teaching chemistry to 11-18 year olds. She blogs at The Chronicle Flask and can also be found tweeting as @ChronicleFlask.