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Welcome to the BMJ Open blog. BMJ Open is an open access journal, dedicated to publishing medical research from all disciplines and therapeutic areas.

Find out more about the journal here.

We will be updating the blog with news about the journal, highly accessed papers, press coverage, events and matters of interest in the open access and publishing world, and anything else that catches our eye.

Prolonged sitting, non-fatal self-harm, and institutional mental healthcare: Most read articles in May

6 Jun, 16 | by Emma Gray

Prolonged sitting and fatigue, non-fatal self-harm, and trends in institutional mental healthcare in Western Europe

File:Une femme lisant à la biblothèque des Champs Libres de Rennes.jpg

This month sees a mixture of some old favourites and some new entries in the Top 10 Most Read list. First up is a pilot study by Wennberg et al which uses a randomised two-condition crossover trial to compare the acute effects of uninterrupted sitting with sitting interrupted by brief bouts of light-intensity walking on self-reported fatigue, cognition, neuroendocrine biomarkers and cardiometabolic risk markers in overweight and obese adults. Kristensen et al‘s paper on the effect of statins remains popular at number two this month and at number four we have an observational study by Geulayov et al which received a press release – it examines trends in non-fatal self-harm and its management in England. In at number five this month is a study by Chow et al investigating how institutional mental healthcare has changed in Western Europe since 1990, finding that there are ongoing overall trends of a decrease in the number of psychiatric hospital beds and an increase in the number of places in other institutions, including prisons. Last month’s most read paper by Gunn et al remains in the top ten, and at number ten we have a new entry by Laver et al with a systematic review of systematic reviews, assessing the effects of interventions to delay functional decline in people with dementia.

Rank Author(s) Title
1 Wennberg et al. Acute effects of breaking up prolonged sitting on fatigue and cognition: a pilot study
2 Kristensen et al. The effect of statins on average survival in randomised trials, an analysis of end point postponement
3 Teschke et al. Bicycling injury hospitalisation rates in Canadian jurisdictions: analyses examining associations with helmet legislation and mode share
4 Geulayov et al. Epidemiology and trends in non-fatal self-harm in three centres in England, 2000–2012: findings from the Multicentre Study of Self-harm in England
5 Chow et al. How has the extent of institutional mental healthcare changed in Western Europe? Analysis of data since 1990
6 Dickstein et al. Multicentre open-label randomised controlled trial to compare colistin alone with colistin plus meropenem for the treatment of severe infections caused by carbapenem-resistant Gram-negative infections (AIDA): a study protocol
7 Martinez Steele et al. Ultra-processed foods and added sugars in the US diet: evidence from a nationally representative cross-sectional study
8 Gunn et al. Prenatal exposure to cannabis and maternal and child health outcomes: a systematic review and meta-analysis
9 Hirono et al. Is health impact assessment useful in the context of trade negotiations? A case study of the Trans Pacific Partnership Agreement
10 Laver et al. Interventions to delay functional decline in people with dementia: a systematic review of systematic reviews

Most read figures are based on pdf downloads and full text views. Abstract views are excluded.

International Clinical Trials Day

19 May, 16 | by aaldcroft

By Sir George Chalmers, c 1720-1791 - [1], Public Domain, https://commons.wikimedia.org/w/index.php?curid=32922810

Today is Clinical Trials Day. Celebrated around the world on or near May 20, Clinical Trials Day commemorates the date when, in 1747, James Lind started the first clinical trial to test citrus fruits as a treatment for scurvy.

This year’s campaign from the NIHR is OK To Ask, which encourages patients and carers to inquire about research opportunities that could be available. We here at BMJ Open support initiatives for patient involvement in research and decision-making and hope that, in making our content freely available online, we help make research more familiar and accessible to the public, including patients, for whom the research is ultimately intended.

While James Lind’s basic principle for the trial remains, the scale, sophistication, and problems surrounding modern trials are evolving rapidly. The importance of registering drugs and publishing all trial results is recognised, but adherence remains unsatisfactory. The notion of what constitutes an intervention is also changing, with text messaging and educational methods now being studied using the same framework as drugs.

BMJ Open will continue efforts to improve the quality of reporting trials, emphasizing the importance of publishing null and negative results and study protocols. The clinical trial is certainly worthy of celebration, along with improvement.

Celebrating International Nurses Day #IND2016

12 May, 16 | by Emma Gray

 

International Nurses Day, celebrated on 12th May each year and coinciding with Florence Nightingale’s birthday, marks the important contributions nurses make to society. As the single largest group of health professionals, nurses care from the first moments of life right through to the final days. To show our appreciation of the work that nurses do, BMJ Open are joining in the celebrations today with a round-up of some of our most popular papers on nursing.

Published in 2015, Dall’Ora et al surveyed registered nurses across 12 European countries to find associations between working 12 hour shifts and job satisfaction, burnout and intention to leave. Receiving over 10,000 downloads since publication, this paper has some important conclusions, finding that longer work hours were indeed associated with adverse outcomes – not only for nurses but potentially for patients as well.

Also published last year was a cross-sectional study into the prevalence of workplace violence that nurses have encountered in Chinese hospitals. The authors, Jiao et al, found that a total of 7.8% of the nurses interviewed for the study had experienced physical violence at work in the previous year, and 71.9% reported experiencing non-physical violence. They aimed to identify risk factors and provide a basis for future interventions, concluding that preplacement education for high-risk groups should take place to reduce workplace violence, and increased awareness from the public as well as policymakers is necessary to develop effective control strategies at individual, hospital and national levels.

One of our most popular papers this year, receiving a press release and over 7,000 downloads since its publication in February, is the paper ‘Registered nurse, healthcare support worker, medical staffing levels and mortality in English hospital trusts: a cross-sectional study’ by Griffiths et al.  Aiming to examine associations between mortality and registered nurse staffing in English hospital trusts, the authors found that ward-based registered nurse staffing is significantly associated with reduced patient mortality, as are higher doctor staffing levels. They conclude by saying that current policies and practices on the staffing in hospital wards should be reviewed in line with the evidence, to reduce risks to patients.

A paper by Schlicht et al published back in 2013 sought to determine the safety and acceptability of the Australian TrueBlue model of nurse-managed care of depression in patients with diabetes or heart disease in the primary healthcare setting. Using a mixed methods study involving a clinical record audit as well as focus groups and interviews with nurses, the study found that nurses were able to identify, assess and manage mental health risks in patients with diabetes or heart disease.  The nurse consultations also meant that there was an opportunity for patients to set goals, as they received scheduled follow-up visits and were monitored regularly, leading to stepped care when appropriate.

The final paper in this short overview of our content on nursing is a review of the cost-effectiveness of nurse practitioners in primary and specialised ambulatory care. A systematic review of randomised controlled trials, conducted by Martin-Misener et al, found that nurse practitioners in alternative provider ambulatory primary care roles have equivalent or better patient outcomes than comparators and are potentially cost-saving. This evidence is promising, but there are few studies contributing to this evidence base at the moment: the authors conclude that while some evidence indicates nurse practitioners in complementary specialised ambulatory care roles improve patient outcomes, their cost-effectiveness requires further study.

More on International Nurses Day:

BMJ is offering free content and discounts on resources for nursing professionals until 12th June: 

To join in with the celebrations, tweet today to show appreciation of nurses using the hashtags #thankanurse #IND2016 and #InternationalNursesDay

Radiotherapy during surgery could save millions of travel miles and tonnes of CO2

9 May, 16 | by Emma Gray

…plus free up thousands of hours for women with early stage breast cancer, every year

One targeted dose of radiotherapy given during surgery to remove early stage breast cancer could save millions of travel miles, enough CO2 emissions for a 100 hectare forest, and free up thousands of hours of women’s time, concludes research published in the online journal BMJ Open.

Standard treatment for early stage breast cancer is surgical removal of the cancerous tissue (lumpectomy), followed by a course of (external) radiotherapy beamed onto the affected breast every day for between three and six weeks.

But single dose targeted intraoperative radiotherapy, or TARGIT for short, is delivered by an applicator directly into the breast tissue during surgery. This adds around 20 to 40 minutes to the operating time, but in most cases avoids the subsequent need for daily hospital visits to complete a standard course of radiotherapy.

Previous international research (TARGIT-A trial) indicates that TARGIT is as good as standard external beam radiotherapy (EBRT) in suitable patients with early stage disease, and it is routinely offered as a treatment option in many countries, say the researchers. But TARGIT is not yet widely available in the UK’s 62 hospitals with radiotherapy units.

To assess the travel implications, journey times, and environmental impact of TARGIT and EBRT, the researchers compared these factors in 485 patients who had taken part in the TARGIT-A trial, 249 of whom had been randomly assigned to TARGIT and 236 to EBRT.

They also included a further 22 patients treated with TARGIT in two other semi-rural centres after the trial had finished.

They calculated the shortest driving distance from home to the radiotherapy unit and average travel time, excluding traffic delays, using Google Maps. They then calculated the total distance travelled and time spent to complete the entire course of radiotherapy.

On average, TARGIT-A trial participants in the UK live 13 miles (21 km) from a radiotherapy unit, and accounting for population density, the researchers estimated that two thirds of the UK population lives further away than this.

CO2 emissions were estimated for a standard family car with an average fuel consumption of 40 miles/gallon (7 litres/100 km). This would produce 299 g/mile (186 g/km) of CO2 emissions for a diesel car and 272 g/mile (169 g/km) for a petrol vehicle.

The TARGIT patients travelled significantly fewer miles (21,681) than EBRT patients (92,591) for their treatment, and spent significantly less time in transit: 3 hours compared with 14 hours.

Their journeys also emitted significantly less CO2: 24.7 kg compared with 111 kg for the EBRT patients.

The researchers worked out that the patients treated in the two semi-rural radiotherapy units each saved themselves journeys adding up to 753 miles, 30 hours of travel time, and they spared the planet 215 kg of CO2.

There are around 50,000 cases of breast cancer diagnosed in the UK every year, of which around three quarters are treated with lumpectomy and EBRT.

Based on these figures, the researchers calculate that if TARGIT became widely available across the UK,  it could save 5 million miles (800,000 km) in journeys, 170,000 hours of travel time, and 1200 tonnes of CO2—equivalent to a forest of 100 hectares—every single year.

This is a lot ‘greener’ than the estimated environmental benefits of introducing mobile breast cancer screening, they say.

“The management of breast cancer has changed over the decades. However, the requirement of patients to travel to receive these specialist services is often forgotten by policy-makers,” they write.

And they conclude that “introducing TARGIT as an option for appropriate patients in the UK will contribute significantly to saving patients time, cost, fuel and CO2 emissions.”

Prenatal exposure to cannabis, overdiagnosis, and counterfeit medicines: Most read articles in April

9 May, 16 | by Emma Gray

Prenatal exposure to cannabis, public definitions of overdiagnosis, and counterfeit medicines in Peru

File:Swanger vrou2.jpg

The Top 10 Most Read papers list this month contains a number of new entries, many of which have been published within the current issue. They come from a wide range of of areas and some have attracted attention via press release, blogs and discussion online. In the top spot is a systematic review and meta-analysis by Gunn et al which was published with an accompanying press release at the start of the month, assessing the effects of use of cannabis during pregnancy on maternal and fetal outcomes. In at numbers 3 and 5 respectively are Medina et al with a retrospective review on drug alerts related to counterfeit medicines in Peru; and Hirono et al, who explore the usefulness of health impact assessment in trade negotiations. Complete with an interview with the lead author on the BMJ Open blog, Ghanouni et al enter the list at number 8 with their survey of public definitions of the term ‘overdiagnosis’ in the UK, and Esch et al examine patient engagement through open notes at number nine. Making it in at number ten this month is a cross-sectional study on polypharmacy by O’Dwyer et al, which evaluates polypharmacy in older people with intellectual disability, compared with the general population.

Rank Author(s) Title
1 Gunn et al. Prenatal exposure to cannabis and maternal and child health outcomes: a systematic review and meta-analysis
2 Kristensen et al. The effect of statins on average survival in randomised trials, an analysis of end point postponement
3 Medina et al. Counterfeit medicines in Peru: a retrospective review (1991-2014)
4 Martinez Steele et al. Ultra-processed foods and added sugars in the US diet: evidence from a nationally representative cross-sectional study
5 Hirono et al. Is health impact assessment useful in the context of trade negotiations? A case study of the Trans Pacific Partnership Agreement
6 Teschke et al. Bicycling injury hospitalisation rates in Canadian jurisdictions: analyses examining associations with helmet legislation and mode share
7 Boulton et al. How much sugar is hidden in drinks marketed to children? A survey of fruit juices, juice drinks and smoothies
8 Ghanouni et al. Survey of public definitions of the term ‘overdiagnosis’ in the UK
9 Esch et al. Engaging patients through open notes: an evaluation using mixed methods
10 O’Dwyer et al. Factors associated with polypharmacy and excessive polypharmacy in older people with intellectual disability differ from the general population: a cross-sectional observational nationwide study

Most read figures are based on pdf downloads and full text views. Abstract views are excluded.

Hospital self-harm cases have steadily risen among men in England since 2008

28 Apr, 16 | by Emma Gray

But only half of those going to hospital afterwards get mental health assessment

The number of hospital cases of self-inflicted harm, such as cutting and overdosing on prescription meds, has risen steadily since 2008 in England among men, reveals research published in the online journal BMJ Open.

But only around half of those who go to hospital after the incident receive a specialist mental health assessment, as national guidelines stipulate they should, the data show.

This is of particular concern as episodes of self-harm precede death in one in every two cases of suicide, the researchers point out.

The researchers base their findings on reported cases of self-harm among people aged 15 and older at five general hospitals in the cities of Oxford, Manchester, and Derby between 2000 and 2012. Self-harm includes intentional injury and overdosing on prescription drugs.

The three cities are all part of the Multicentre Study of Self Harm in England. Because they are socially and economically diverse, the study participants are reasonably representative of urban patterns of self-harm across the country, say the researchers.

During the 13-year study period, 84,378 episodes of self-harm involving 47,048 people were dealt with at the five hospitals. Well over half of these cases (58+%) were among women.

Almost four out of 10 people were under 25, and nearly two thirds (62%) were under 35. Almost a third (30%) were receiving some form of psychiatric care when they self-harmed.

Overall, rates of self-harm fell among women from 2000 onwards. They also fell in men, but only until 2008, after which they steadily rose, possibly because of the effects of the economic downturn, suggest the researchers.

The rates of self-harm closely mirrored patterns of suicide seen in the general population, for both men and women.

An intentional overdose was responsible for more than three quarters of the episodes. Of these, common painkillers were used in over half the overdoses, while antidepressants were used in one in four (just under 25%).

Benzodiazepines, a class of drugs used to treat anxiety and sleep problems, were used in around one in seven cases (just under 14%), while major tranquilisers and antipsychotics were used in around 7% of cases.

A sharp increase in reported cases of cutting/stabbings and hanging/strangulation occurred in the second half of the study period.

“It should be noted that there is a stronger risk of suicide following self-cutting compared to self-poisoning,” write the researchers, adding: “Also repetition of self-harm is more common in individuals who cut themselves.”

One in four people self-harmed again within a year.

Overall, the proportion of people getting a specialist mental health assessment following their visit to hospital was greater in 2012 than in 2003, although this varied among the five hospitals.

Nevertheless, only just over half (53%) of 67,653 episodes of self-harm were followed up with a mental health assessment, as recommended in 2004 by the National Institute of Health and Care Excellence (NICE).

This was particularly true of people who cut themselves, with only just over a third (38%) of those who chose this method receiving an assessment, compared with more than 56% of those who overdosed.

“Our finding that only a little over a half of individuals presenting to hospital after self-harm were offered psychosocial assessment and that individuals who self-injured were least likely to receive an assessment, coupled with the rise in self-injury as a method of self-harm, and the link between such methods and suicide, may have important implications for the management of self-harm in hospitals,” suggest the researchers.

Metal hip replacements implanted since 2006 more prone to failure

28 Apr, 16 | by Emma Gray

Higher rate of issues in manufacturing process since this date may be to blame, say researchers

Metal on metal hip replacements implanted since 2006 are more prone to failure and the need for further surgery, finds research looking at revision rates at one hospital trust for the DePuy Pinnacle device, and published in the online journal BMJ Open.

A higher rate of manufacturing issues since 2006, with more than a third of hips manufactured outside the stated specifications, may be to blame, suggest the researchers.

They looked specifically at the long term performance of the 36 mm Pinnacle metal on metal hip—the most commonly implanted metal hip in the world—in a bid to uncover the risk factors associated with early failure and the need for further surgery.

The use of metal on metal hips has plummeted over the past five years, but “hundreds of thousands” remain in place. A better understanding of the factors associated with a higher risk of failure would not only help those patients fitted with them, but could also inform the design of future products, say the researchers.

They reviewed the progress of 434 patients (243 women and 191 men) fitted with 489 metal on metal total hip replacements at one hospital trust in northern England, and monitored for an average of 7.5 years after the procedure.

In all, 71 metal hips required surgical removal and replacement, adding up to a revision rate of 16.4%, which the researchers describe as “unacceptably high.”

A metal on metal hip consists of a metal ‘ball,’ which acts as the top of the thigh bone (femoral head). This fits inside a metal liner, which acts as the replacement socket.

Total replacement of both (bilateral) hip joints and thinner liners were risk factors for failure at nine years.

But implantation from 2006 onwards also carried a significantly higher risk of revision, possibly because of the increasing tendency from this date to manufacture devices outside of their intended product specification, say the researchers.

Before 2006, only five out of 43 hips (12%) failed to meet the manufacturer’s product specification. But after 2006 more than a third (36%; 43 out of 118) failed to comply.

Furthermore, in over 40% of cases examined the taper surface was defective. The taper surface describes the inside of the femoral head that is attached to the femoral stem—the part that anchors the implant in the thigh bone. This defect was significantly associated with excessive metal particle release.

Abundant metal staining of tissues visible to the naked eye (metallosis) had occurred in around one in five (19%) cases.

Metal hips implanted into women were also more likely to fail, but the researchers caution that twice as many women as men had bilateral hip replacements, and when the findings were analysed according to sex and liner thickness, thinner liners had the greater impact.

Data from the National Joint Registry for England and Wales for 2014 indicate that 11,871 metal on metal Pinnacle hips have been implanted, prompting the researchers to calculate that 180,000 people around the world are now walking around with these hips. These patients might be at risk of early revision surgery, they suggest.

What is ‘overdiagnosis’? Public meanings and misconceptions

28 Apr, 16 | by Ed Sucksmith

overdiagnosis pic 1

A recent study published in BMJ Open found less than 3% of the British public could define the meaning of overdiagnosis correctly. We talk to lead author Dr Alex Ghanouni about his research.

Stories about the ‘overdiagnosis’ of medical conditions regularly make the headlines. “GPs to trial new tests for asthma amid concerns about overdiagnosis” reported The Guardian in February, whilst in March The Telegraph declared “ADHD is vastly overdiagnosed and many children are just immature”. But what is meant by the term overdiagnosis and is it correctly understood? Some stories equate overdiagnosis with the proliferation of misdiagnoses or so-called ‘false-positives’ where a diagnostic test wrongly indicates that you have a medical condition. These meanings, however, are considered inaccurate by medical experts. They instead define it somewhat counter intuitively as the diagnosis of a disease which would never have become clinically apparent in a person’s lifetime. In other words, the disease is real but it does not cause the patient any harm, whether or not it has been identified through a medical test.

A research group led by Dr Jo Waller from University College London set out to assess the British public’s awareness and understanding of overdiagnosis. Why did Dr Waller and colleagues pursue this particular topic? “Our interest in overdiagnosis came primarily via the debate around its significance in breast cancer screening” explains Dr Alex Ghanouni, a member of the research team. Screening tests for breast cancer may lead to the identification of tumours that would not have presented clinically in the absence of the screening test. Overdiagnosis is therefore a significant concern because it could result in patients receiving unnecessary treatments as well as needless stress and anxiety that arise from receiving a diagnosis. “Knowing that the public often has only limited knowledge about the intricacies of screening tests, we speculated that the term has not reached public awareness, despite intense professional debate. We thought it important to assess this since it would limit people’s ability to consider it when deciding whether to take up a screening invitation.

Dr Waller’s team surveyed 390 adults from the UK aged 50-70 years of age. The survey asked participants if they had seen or heard of overdiagnosis and, if they had, to explain what the term meant. Results revealed that just 3 in 10 participants had encountered the term before, whilst less than 3% of all participants surveyed provided responses that were consistent with the accepted definition. A number of common misconceptions were identified, including equating overdiagnosis with both ‘misdiagnosis’ and ‘false-positive diagnosis’.

The study’s findings attracted a large audience when they were published in March. Were the authors surprised by the level of attention that their study received? “We were surprised in some respects”, says Dr Ghanouni, “In previous studies, we have found that overdiagnosis is something that few people understand intuitively and so we had some expectation that this would make the study less accessible to the general public. On the other hand, we were aware throughout the study that we were researching a topic where there were many strong views among medics and academics and so we did expect a degree of attention, at least among people working in related fields.

The survey results replicated previous studies that found low public knowledge of overdiagnosis in the UK and elsewhere. Dr Ghanouni and colleagues plan to further develop their research in this area. “This is an area of research that we are keen to take further and have in fact just had a paper published on a follow-up topic, namely, of information about overdiagnosis in breast screening that the public can read on the most prominent UK and Australian health websites. Some of our findings were quite striking; for example, we found that a markedly higher proportion of websites included relevant information compared to the last study to review information on the web, in 2002. This might indicate that the topic will gradually become something that more people know about.”

 

More on Overdiagnosis

For further information about overdiagnosis please see The BMJ’s ‘Too Much Medicine’ campaign, which aims to highlight and contribute to the evidence base on overdiagnosis and overtreatment. This includes a recent digital theme issue on overdiagnosis. The BMJ is also a partner in the upcoming Preventing Overdiagnosis conference that will be taking place on 20 – 22 September 2016 in Barcelona, Spain.

Ultra-processed foods, drinks marketed to children, and cannabis use in psychosis: Most read articles in March

8 Apr, 16 | by Emma Gray

Ultra-processed foods and added sugars, the content of drinks marketed to children, and cannabis use in first episode psychosis

File:Unhealthy snacks in cart.jpg

March was a busy month here at BMJ Open, with many new papers entering the Top 10 Most Read. In at number one this month is a popular paper which was press released and saw a lot of activity on Twitter: a cross-sectional study investigating the contribution of ultra-processed foods to the intake of added sugars in the USA. Boulton et al enter the list at number two with a much discussed survey of fruit juices to determine the sugar content of drinks marketed to children, which made national news, and Brown et al review the effectiveness of community pharmacy-delivered interventions for alcohol reduction, smoking cessation and weight management at number five. Investigating the association of cannabis use with hospital admission and antipsychotic treatment failure in patients with first episode psychosis, Patel et al come in at number five. Finally, at number nine we have an interesting analysis of systematic reviews by Elia et al which asks how authors of systematic reviews deal with research malpractice and misconduct in original studies.

Rank Author(s) Title
1 Martinez Steele et al. Ultra-processed foods and added sugars in the US diet: evidence from a nationally representative cross-sectional study
2 Boulton et al. How much sugar is hidden in drinks marketed to children? A survey of fruit juices, juice drinks and smoothies
3 Griffiths et al. Registered nurse, healthcare support worker, medical staffing levels and mortality in English hospital trusts: a cross-sectional study
4 Kristensen et al. The effect of statins on average survival in randomised trials, an analysis of end point postponement
5 Brown et al. Community pharmacy-delivered interventions for public health priorities: a systematic review of interventions for alcohol reduction, smoking cessation and weight management, including meta-analysis for smoking cessation
6 Patel et al. Association of cannabis use with hospital admission and antipsychotic treatment failure in first episode psychosis: an observational study
7 Shyangdan et al. SGLT-2 receptor inhibitors for treating patients with type 2 diabetes mellitus: a systematic review and network meta-analysis
8 Gattrell et al. Professional medical writing support and the quality of randomised controlled trial reporting: a cross-sectional study
9 Elia et al. How do authors of systematic reviews deal with research malpractice and misconduct in original studies? A cross-sectional analysis of systematic reviews and survey of their authors
10 Mekonnen et al. Effectiveness of pharmacist-led medication reconciliation programmes on clinical outcomes at hospital transitions: a systematic review and meta-analysis

Most read figures are based on pdf downloads and full text views. Abstract views are excluded.

Cannabis use in pregnancy linked to low birthweight and intensive care

5 Apr, 16 | by Emma Gray

As drug gains social acceptance, doctors and women need to be better informed, say researchers

Use of cannabis during pregnancy is linked to low birthweight and the need for intensive care, reveals an analysis of the available evidence, published in the online journal BMJ Open.

As cannabis becomes more socially acceptable, it’s important that prospective mums-to-be and clinicians are fully up to speed on the potential harms of using the drug during pregnancy, caution the researchers.

Cannabis “remains the drug of choice in developed and developing countries,” with up to 5% of 15-64 year olds around the world thought to use it, the researchers point out.

While it never used to be a major cause for concern, recent research has pointed to links between the drug and an increased risk of road traffic accidents, psychosis, HIV, hepatitis, infective endocarditis and TB. Less is known, however, about its possible effects on fetal growth and development.

The researchers carried out a comprehensive trawl of seven research databases for studies published up to 2014, looking at the effects of cannabis use during pregnancy on mother and baby up to six weeks after the birth.

Outcomes, such as anaemia in the mother, birthweight, baby’s length, need for neonatal intensive care, head circumference and early birth were all included in the review of 24 studies.

Analysis of the pooled data showed that mums- to-be who used cannabis were 36% more likely to have anaemia than women who didn’t use the drug.

Infants exposed to cannabis in the womb were 77% more likely to be under weight at birth and twice as likely to require intensive care as those whose mums had not used cannabis during their pregnancy.

The research in the analysis included observational studies, making it very difficult to draw firm conclusions about cause and effect. And the researchers were not able to extract data on whether any of the study participants used other illicit drugs or how much alcohol they drank—factors known to be associated with a higher risk of low birthweight and premature birth.

Nevertheless, they conclude: “There does appear to be negative consequences associated with in utero exposure to cannabis, including a decrease in birthweight and a need for placement in [intensive care].”

As the medical and social use of the drug “is rapidly becoming more acceptable in the USA and around the world,” understanding its effects on maternal and fetal health “should become a global priority,” they suggest.

Women and their doctors could do with more information on the possible harms of using the drug during pregnancy, they say.