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Updated: 20 hours 16 min ago

Link between stillbirth and air pollution 'inconclusive'

Wed, 2016-05-25 05:30

"Air pollution may raise risk of stillbirth and pregnant women should consider leaving cities, say scientists," The Daily Telegraph reports.

This is somewhat radical advice given the study that prompted the headline produced no significant or conclusive results.

Stillbirth is when a baby dies before birth, but after 24 weeks of pregnancy. There are about 3,600 stillbirths every year in the UK. It is a rare but devastating outcome, and it can be difficult to know why it's happened.

Possible risk factors include infection during pregnancy, maternal smoking, maternal alcohol consumption, or having twins or multiple pregnancies. Often there is no obvious reason why a stillbirth happened.

Scientists don't know whether air pollution is linked to stillbirth. This study was carried out to summarise all the research on the subject so far. But the results are still unclear.

The pooled risks from the different studies showed a small increase in the chances of stillbirth if a woman lived in an area with raised pollution levels. But the increases in risk were so small that they could be down to chance.

While air pollution is clearly not good news for anyone's health, and governments should do all they can to reduce it, this study does not prove that it causes stillbirth. Impractical and unrealistic advice that pregnant women should move out of cities does not help anyone.

Where did the story come from?

The study was carried out by researchers from the University of Oulu, Finland, and the University of Cape Coast, Ghana, and was funded by the University of Oulu. 

It was published in the peer-reviewed journal Occupational Environmental Medicine on an open-access basis, so you can read it for free online.

The Telegraph and the Daily Mail both led on comments from one of the researchers that it would be "wise advice" to tell a pregnant woman to move to a greener area, without discussing how realistic or practical such advice actually is for most mums-to-be.

The news stories also fail to explain that the findings of this study were not statistically significant, meaning they could have been the result of pure chance.

The Independent and the Daily Mirror give more cautious views of the research and include comments from other experts, which balance their reporting.

What kind of research was this?

This was a systematic review and meta-analysis of observational studies, including cohort studies and case control studies aiming to gather evidence to see whether there may be a link between air pollution and stillbirth.

Systematic reviews are good ways of summarising the state of evidence on a topic, but they are only as good as the studies they include.

There is always a possibility with observational studies that other confounding factors – such as the health and lifestyle of the individual woman – could bias the results.

What did the research involve?

Researchers searched for studies that looked at air pollution, including a wide range of air pollutants, and stillbirths.

They included observational studies that gave information about mothers' estimated exposure to pollution (based on where they lived) and pregnancy outcomes.

They then pooled the data for different types of pollutants to see whether any of them were linked to a raised risk of stillbirth.

Most of the studies used data from air pollution monitoring stations and death certificates. Most balanced the results for confounding factors, such as the women's age and health.

Some adjusted their results to take account of the effects of other types of pollution, although most did not. Some adjusted for factors like the time of year and weather, which can affect pollution concentrations.

The researchers carried out a meta-analysis of the effect of each of six types of pollutant on the risk of stillbirth. The studies covered 11 types of pollutant, but there was not enough comparable information to do a meta-analysis on all types.

What were the basic results?

None of the six pollutants studied showed a clear risk of stillbirth. The pollutants included were:

  • sulphur dioxide
  • nitrogen dioxide
  • carbon monoxide
  • course particulate matter (PM10)
  • fine particulate matter (PM 2.5)
  • ozone

All the pollutants were linked to an increased risk when levels were higher than average, but this raised risk was too small to be sure it was not down to chance – in other words, it was not statistically significant.

In each case, the results' "95% confidence intervals" included the possibility that the raised pollution levels had no effect on risk of stillbirth.

This was true for each of the pollutants studied at every stage of pregnancy. The results showed the effect of stage of pregnancy differed from one pollutant to another, so in some the possible risk was higher in the first trimester and in others it was higher in the third trimester.

How did the researchers interpret the results?

The researchers say they found "suggestive evidence" that air pollution is a risk factor for stillbirth.

They say pregnant women "should be aware" of this risk, but that the main action required is by governments to reduce pollution levels.

They do not state in the paper itself that pregnant women should move to the countryside.


Pregnancy can be an anxious time for women – well-meant but alarming advice about possible risks to your unborn baby is not always helpful.

It's difficult to know what to make of a paper with inconclusive findings, like this one. As one expert says: "A reasonable headline for a press release on this work could have been 'Air pollution and stillbirth – we still don't know whether they are linked'."

The quote comes from Professor Kevin Conway, professor of applied statistics at the Open University, who concludes: "I don't think these new findings should be a serious cause for concern for individual pregnant women – if there is an increased risk of stillbirth, this review indicates that the increase is pretty small."

To put the risk into context, several of the pollutants studied were associated with a non-significant risk increase of around 2%. The non-significance means there's no evidence for a link, but even if there is one, it seems the risk increase from air pollution is likely to be very small.

Compare to this the findings of a previous systematic review, which found that secondhand smoke exposure increased stillbirth risk by 23% – and this time it was a significant link.     

However, Professor Conway and other experts agree that pollution and the potential risk of stillbirth are important topics to investigate, and future studies should be carried out to look at this area.

While the study doesn't show that pollution definitely causes stillbirth, it doesn't rule out the possibility.

One issue that needs to be addressed in future research is an accurate assessment of how much pollution individual women breathe in.

The studies assessed women's pollution exposure based on where they lived in relation to the nearest air quality monitoring station.

For some women, that was up to 25km away, so the levels monitored at the station may not reflect the quality of the air women were breathing.

Other studies have shown that just moving one street back from a busy road can make a big difference to your exposure to pollution.

We also don't know enough about the women's lives – where they worked, whether they travelled away from their homes, or what the air quality was like in their houses or workplaces.

Another major problem with the study is that even if scientists did show a strong link to pollution, we don't know whether this might have been caused by other confounding factors.

For example, people living in more polluted areas might have poorer health for other reasons, such as taking less exercise or having less money to spend on healthy food.

Finding out whether air pollution might be a cause of stillbirth is not easy. It's good that scientists are doing this research and making an effort to find out about the effects of air pollution. So far, however, we don't have enough reliable information to know its effects for sure.

The researchers' suggestion that pregnant women should consider moving to the countryside, as reported by the media, cannot be supported based on the evidence seen here. Aside from the impracticalities, moving house while pregnant could add unneeded stress during a pregnancy.

The most effective steps you can take to reduce your risk of having a stillbirth are to avoid smoking and drinking and be cautious of sources of infections known to be harmful.  

Links To The Headlines

Air pollution may raise risk of stillbirth and pregnant women should consider leaving cities, say scientists. The Daily Telegraph, May 25 2016

Pregnant women 'should consider moving to the countryside' because air pollution may raise the risk of stillbirth, doctors warn. Daily Mail, May 25 2016

Air pollution could increase risk of stillbirth, research suggests. The Independent, May 25 2016

Stillbirth risk increased by exposure to air pollution caused by car and industrial emissions, warn experts. Daily Mirror, May 24 2016

Links To Science

Siddika N, Balogun HA, Amegah A, et al. Prenatal ambient air pollution exposure and the risk of stillbirth: systematic review and meta-analysis of the empirical evidence. Occupational and Environmental Medicine. Published online May 24 2016

Categories: News

Proof opiates are useful for chronic back pain 'lacking'

Tue, 2016-05-24 06:30

"Powerful painkillers doled out in their millions are ineffective against back pain," the Daily Mail reports.

An Australian review found evidence for the effectiveness of opiate-based painkillers, such as tramadol and oxycodone, for chronic back pain was "lacking".

The review pooled the findings of 20 trials investigating the safety and effects of opioid painkillers for non-specific or mechanical chronic lower back pain.

This is back pain with no identified cause, such as a "slipped" disc or injury. This is a common, yet poorly understood, type of back pain that is often challenging to treat.

The trials found opioids had a minimal effect on pain compared with an inactive placebo – about half the level that would be needed for a clinically meaningful effect.

The rate of intolerance was also very high, with often half or more people experiencing side effects like nausea and constipation, and withdrawing from treatment as a result.

The findings lend support to national guidelines for the management of non-specific lower back pain, which suggest it is inadvisable for a person to rely solely on painkillers.

Self-management techniques, such as education, exercise programmes, manual therapy and sometimes psychological interventions, may deliver greater lasting benefits.

If pain relief is needed, weaker painkillers, such as paracetamol, and anti-inflammatory drugs, such as ibuprofen, are advised initially, with strong opioids only used for a short period of time for severe pain.  

If you are having trouble coping with chronic pain, contact your GP, who may be able to recommend additional treatments and services.

Where did the story come from?

The study was carried out by researchers from the George Institute for Global Health at the University of Sydney, and other institutions in Australia.

Funding was provided by the Australian National Health and Medical Research Council.

The review was published in the peer-reviewed journal JAMA Internal Medicine on an open-access basis, so it is free for you to read online.

The Mail's reporting of the study was generally accurate, but the headline in the print version of its story – "Back pain drugs 'do more harm than good'" – is unsupported.

The study only considered short-term side effects such as nausea and constipation, and not the longer-term problems addressed in the paper's reporting, like addiction and overdose.

What kind of research was this?

This systematic review and meta-analysis pooled the results of randomised controlled trials, aiming to see whether opioid painkillers such as codeine, tramadol and morphine are safe and effective for managing lower back pain.

Although people with chronic lower back pain may often resort to the use of opioids because lesser painkillers are ineffective, the researchers say there has been no systematic study examining their effects and tolerability at different doses.

A systematic review is the best way of gathering the available evidence to look at safety and effectiveness, but the strength of a review's findings are only as good as the studies it includes.

What did the research involve?

The researchers searched several literature databases to identify randomised controlled trials of opioid use in people with non-specific lower back pain.

Sometimes called mechanical lower back pain, this is back pain where no specific cause can be identified, such as a herniated, or "slipped", disc, inflammatory conditions, infection, or cancer, for example.

Trials were eligible if they compared an opioid with inactive placebo, or compared two different drugs or doses, and reported outcomes of pain, disability or adverse effects.

There were no restrictions on the duration of back pain, painkiller use, use of other medications, or the presence of other illnesses. Two researchers reviewed and quality assessed studies, and extracted data.

The trials included rated pain on visual or numerical scales (for example, rating pain from 0 to 100) and disability scores on questionnaires such as the Roland Morris Disability Questionnaire and Oswestry Disability Index.

The researchers reported the mean difference in scores between the opioid and control groups. A difference of 10 points on a 100-point scale was a minimal difference required for any effect on pain, but a 20-point difference was considered a clinically meaningful effect.

The researchers were mainly interested in short-term effects on pain relief. They also looked at the number of people who withdrew from the trial or were lost to follow-up as a result of adverse effects or lack of effect.    

Twenty trials involving 7,295 people were identified, 17 of which compared opioids with placebo, while two compared opioids with each other.

All the trials examined effects in the short term only – the maximum treatment and follow-up period was three months. The trials were generally high quality. 

What were the basic results?

The pooled results of 13 studies (3,419 people) found opioids had a minimal effect on pain – there was a mean 10.1 score difference between opioids and placebo (95% confidence interval [CI] 7.4 to 12.8 reduction).

The difference when using single-ingredient opioids was 8.1, and 11.9 when using an opioid combined with another simple painkiller, like paracetamol.    

There was limited data available for disability. Two studies found the combination of tramadol and paracetamol had no effect on disability compared with placebo, while another found no effect for morphine. However, the quality of evidence for these outcomes was said to be very low.

The researchers looked at studies with a run-in period separately. This is where only those who responded favourably during the trial phase were actually randomised. Such trials therefore preferentially only include good responders.

These results found increasing opioid dose was associated with better pain relief, but clinically meaningful effects on pain were still not seen at any of the doses evaluated.

When looking at the two head-to-head trials directly comparing two opioids/doses, both trials found around a five-point score difference.

The proportion of participants who withdrew was high in all trials – up to around 50% or greater withdrew.

The main cause for withdrawal was lack of effect or adverse effects. More than half the people taking opioids experienced side effects such as nausea, constipation and headaches. 

How did the researchers interpret the results?

The researchers concluded: "For people with chronic low back pain who tolerate the medicine, opioid analgesics provide modest short-term pain relief, but the effect is not likely to be clinically important within guideline recommended doses." 


This systematic review found no evidence that opioids provide a meaningful effect on chronic non-specific lower back pain.

Opioids are often used as a last resort for people who have not responded to other painkillers. But these results found opioids gave only half the size of the effect that would be needed to make a real difference – about a 10-point score difference, rather than 20.

On the whole, the body of evidence was high quality. A large number of trials where identified, and most were multi-centre trials with good sample sizes carried out in the US, Canada, Australia and Europe. This means the findings should be representative of people with this condition in the UK.

Most of the evidence compared the effect of opioids with placebo only, rather than any other active intervention.

And 17 of the studies were funded by the pharmaceutical industry, giving uncertain potential for publication bias.

However, in these cases, if anything, you would expect to see an overly favourable effect of opioids, which is not the case.  

The extremely high dropout rate also cannot go unnoticed – 50% or greater in many studies.

This may have contributed to the lack of effect seen, but also demonstrates the difficulty there is tolerating these strong painkillers. Many people experience debilitating side effects when taking them, such as nausea, vomiting and constipation.  

Chronic non-specific lower back pain is an extremely common cause of disability in the UK. Perhaps overreliance on pain killers and anti-inflammatory drugs isn't the best answer.

As the guideline body the National Institute for Health and Care Excellence (NICE) says, a key focus should be on helping people manage their condition themselves through education and information, exercise programmes, or manual therapy.

Chronic non-specific pain can sometimes also have a psychological element, and interventions such as cognitive behavioural therapy can be helpful.

NICE recommends regular paracetamol as the first-choice option for pain relief. If this is insufficient, they suggest moving to non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, or weak opioids, such as codeine, but being aware of the potential side effects of both.

Stronger opioids, such as fentanyl or oxycodone, are only advised for short-term use for severe pain.     

These recommendations, and the findings of this review, do not apply to people with identified causes of their back pain, such as inflammatory conditions, infections, cancer, or trauma. 

If you have been taking opiate-based painkillers for some time and feel you no longer need or want to take them, you should talk to your GP. Stopping suddenly is not a good idea as this could trigger withdrawal symptoms.

For more information, visit the NHS Choices guide to back pain.

Links To The Headlines

Powerful painkillers for back pain like morphine and tramadol are 'NOT effective and can be dangerous'. Daily Mail, May 23 2016

Links To Science

Shaheed CA, Maher CG, Williams KA, et al. Efficacy, Tolerability, and Dose-Dependent Effects of Opioid Analgesics for Low Back Pain. JAMA Internal Medicine. Published online May 23 2016

Categories: News