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expert reaction to study looking at smoking and vaping in pregnancy and infant behaviour

A study, published in EClinicalMedicine, has looked at smoking and vaping in pregnancy and infant behaviour.


Prof Jamie Brown, Professor of Behavioural Science and Health, and Director of the Tobacco and Alcohol Research Group, UCL, said:

“It is well-established that cigarette smoking during pregnancy increases the risk of a range of health problems.  It is important to establish the risk of e-cigarettes compared with cigarettes during pregnancy.  This requires studies to conduct a detailed assessment of both these behaviours during pregnancy.  We know that most e-cigarette users have previously smoked.  It is not clear from this article how much the 10 parents who switched to e-cigarettes by 32 weeks had smoked before that point nor the extent to which cigarette smoking during the pregnancy may have been responsible for the findings.  It is notable that twenty percent of the people using e-cigarettes at 32 weeks in this study had relapsed to cigarette smoking by birth.”


Prof Michael Ussher, Professor of Behavioural Medicine, St George’s, University of London and University of Stirling, said:

“A major concern with this study is that the authors only assessed whether the e-cigarettes users had smoked cigarettes in recent hours, rather than also in recent days or weeks.  Dual use of cigarettes and e-cigarettes is fairly common in pregnancy and it is possible that the observed harms are due to smoking among those in the e-cigarette group.  Also, it is incorrect to use the term ‘smoking e-cigarettes’ as there is no smoke in vapour.  The evidence remains that smoking cigarettes is far more harmful than vaping and vaping may help women to stop smoking.”


Prof Linda Bauld, Professor of Public Health, University of Edinburgh, said:

“This small study involved 83 healthy babies around one month old whose neurobehavioural responses (things like reflexes, i.e. the ability to grasp a caregiver’s finger and self-regulation including being relaxed when held) were assessed.  The researchers compared babies whose mothers had a) smoked during pregnancy b) used e-cigarettes during pregnancy c) neither smoked nor vaped.  The authors begin by explaining that neurobehavioural problems observed in babies of mothers who smoke might also be present in those who vape and that the mechanism for this may be nicotine, which is present in both cigarettes and (most) e-cigarettes.

“The authors reported that the babies born to mothers who had smoked or vaped had abnormal reflexes and slightly decreased self-regulation compared to those of babies whose mothers had not used either product.  They suggest this might mean that these babies may have signs of impaired brain development and as a result women should not use e-cigarettes in pregnancy.

“The authors are correct that little is known about how vaping in pregnancy affects babies and infants.  However, we should be cautious when assuming this study proves that vaping in pregnancy harms babies.  The first reason to be cautious is that their hypothesis that it is the nicotine in e-cigarettes that may be to blame is not supported by previous research in humans.  The large SNAP trial found that young children whose mothers had used nicotine replacement therapy after stopping smoking in pregnancy had normal development up to two years old.

“The second reason is that women who vape in pregnancy are almost universally ex smokers and it is not uncommon for these women to gradually shift to vaping or even smoke and vape in pregnancy.  Vaping was simply self-reported in the study and smoking status was only assessed once at 32 weeks pregnant.  It is therefore possible that some or even all of the vaping mothers may have smoked even at low levels at some point during their pregnancy, and if they did this would be a significant confounder, making the results difficult to interpret.  The authors do not even mention this important (and likely) limitation in their article.  Finally it is important to note the small size of the vaping group – just 10 women.  That sample size is not sufficient to draw firm conclusions.

“There are also some questions to be asked about basic errors in the paper.  For the demographic information, carbon monoxide (CO) readings are used to validate smoking status and the paper says that this translates to the % of CO in the maternal blood.  But CO screening involves a breath test not a blood test.  In addition the authors refer to ‘e-cigarette smoking’ throughout the paper.  There is no smoke or tobacco in e-cigarettes and these devices are not ‘smoked’.  These two features suggest the authors are not familiar with the literature in this area and are issues that should have been picked up when the paper was peer-reviewed.”


Prof John Britton, Emeritus Professor of Epidemiology, University of Nottingham, said:

“This is a poor study for several reasons – it isn’t randomised; there is no power calculation; there are only 10 e-cig users and two of them reverted to smoking before the babies were tested; the paper presents p values instead of effect sizes; some of the outcome scores are clearly not normally distributed (mean – 2SDs is less than 0 in a score with a minimum of zero) but are treated as such; the level of Bonferroni correction for multiple comparisons is not explained (and there are multiple comparisons); and it compares 17 outcomes, three ways, with only 10 (or even really only 8) people in one of the groups.

“The authors suggest their paper raises the possibility that using nicotine in pregnancy may reduce reflex responses in newborn children.  While this remains a possibility, if their study does suggest this then it also demonstrates clearly that babies born to mothers who smoke are harmed to a considerably greater extent than any possible harm from nicotine use.  It does not therefore change current advice to pregnant women who smoke, which is to quit all nicotine use if possible but at the very least, stop smoking tobacco.”



‘The effects of prenatal cigarette and e-cigarette exposure on infant neurobehaviour: A comparison to a control group’ by Suzanne Froggatt et al. was published in EClinicalMedicine at 00:01 UK time on Friday 16 October 2020.

DOI: 10.1016/j.eclinm.2020.100602


Declared interests

Prof Jamie Brown: “JB has received unrestricted funding to conduct smoking cessation research from pharmaceutical companies who manufacture smoking cessation medications. He has not and would not receive funding from the e-cigarette or tobacco industry.”

Prof Michael Ussher: “I have no COIs.”

Prof Linda Bauld: “Professor Bauld co-chairs the Smoking in Pregnancy Challenge Group that has developed resources on smoking and vaping in pregnancy in partnership with the Royal College of Midwives, the Royal College of Nursing and other Challenge group members.”

None others received.

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