text: E-cigarette risks in pregnancy
  In this article:
  - Vaping in pregnancy - what we know
  - Nicotine in pregnancy
  - E-cigarettes in pregnancy
  - Dual use
  - Main points
  Vaping in pregnancy – what we know
  “E-cigarettes” or Electronic Nicotine Delivery Systems (ENDS) simulate the smoking experience by “vaping” a mist which contains water, propylene glycol, vegetable glycerine, and usually nicotine and a range of more than a thousand flavourings. As e-cigarettes have only been widely used for a few years, uncertainty remains regarding the effectiveness of e-cigarettes as a smoking cessation tool when compared with conventional nicotine replacement therapy (NRT).
  Recent studies have found “positive” findings in ideal conditions, however users were 30% less likely to successfully quit in many observational studies1 than users undertaking conventional methods. Further uncertainty exists around the risk profile of e-cigarettes themselves, however in the UK, the Faculty of Public Health, Association of Directors of Public Health, and Public Health England2 all agree that e-cigarettes are likely to be less harmful to health than conventional smoking in those who cannot otherwise quit.
  However, this may not translate to the same advice in pregnant women because nicotine (present in e-cigarettes) itself is harmful to the unborn child. As the evidence surrounding e-cigarettes in pregnancy is in its infancy, information for pregnant women and their partners can be less available during pregnancy compared to conventional smoking cessation tools. Here we outline what is currently known regarding the risks of e-cigarettes in pregnancy.
  Nicotine in pregnancy
  It is understood that nicotine from smoking accounts for the largest proportion of decline in gestational age, whilst other toxins in cigarettes account for the largest proportion of reduction in birth weight attributable to smoking during pregnancy3.It is therefore stated and agreed that there is no “safe” level of nicotine during pregnancy4.Nicotine has been associated with harm to the development of several organs. This includes lung function development5, as well as impairment of the functions of the endocrine, reproductive, cardiovascular and neurological systems6.Nicotine consumption during pregnancy has also been associated with increased incidence of Attention Deficit Hyperactivity Disorder (ADHD), aggressive behaviour and future substance abuse6.
  Nicotine replacement therapy (NRT) is a medically-approved way to take nicotine by means other than tobacco in those who are unable to quit entirely. NRT is used to help smoking cessation and increases the chances of successfully quitting smoking by approximately 50-70%. Conventional NRT therefore still poses a risk to the unborn child given its nicotine composition, however this is at a lower risk than cigarette smoking.
  NRT is therefore used for pregnant women who are unable to quit without this assistance and is utilised alongside counselling to educate mothers that although risk is reduced compared to smoking cigarettes, risk is not as low as non-smokers and non-NRT users altogether. Therefore, the nicotine content in e-cigarettes is important when assessing the risk profile in pregnancy.
  E-cigarettes in pregnancy
  Given the relative infancy of the evidence base for e-cigarettes, it is unsurprising that there are no randomised controlled trials, nor good observational evidence assessing e-cigarettes in pregnancy to date7.The nicotine concentration in e-cigarette use is less than through smoking conventional cigarettes8.Typical serum concentrations peak at approximately 1.3 ng/mL after 20 minutes vaping compared to 2.1 ng /mL 30 minutes after using a nicotine inhaler and 13.4 ng/mL after 15 minutes of smoking a conventional cigarette9.
  There is therefore consensus that e-cigarettes deliver lower nicotine doses than conventional cigarettes, however nicotine doses compared to conventional NRTs is less clear due to the large variability of nicotine doses in different e-cigarettes. This is likely to become clearer in time as better evidence emerges and regulations develop. This has already begun.
  For example recent regulations in the UK have been introduced stipulating that the nicotine dose must be labelled on e-cigarettes10.Whilst there are no interventional studies assessing e-cigarettes in pregnant humans, there have been some interventional studies in mice. Here, exposure to e-cigarettes for the first 10 days of life resulted in a modest impairment of lung growth and a 13% reduction in body weight compared to control mice exposed to room air instead of e-cigarettes11.These results clearly can’t be directly translated to humans, however they are consistent that e-cigarettes are unlikely to be risk-free in pregnancy and urge us to exercise caution.
  It is important that pregnant women and healthcare professionals are aware of the potential dangers of ‘dual use’ where e-cigarettes are used in addition to, rather than instead of, conventional cigarettes. Dual use increases the total nicotine dose for the smoker, and in turn the fetus.
  Evidence is evolving constantly for e-cigarettes owing to their infancy; however to date, the evidence suggests that e-cigarettes are likely to post a lower risk than conventional smoking in the general population. However, as e-cigarettes contain nicotine, there is currently insufficient evidence to suggest that e-cigarettes are safe in pregnancy, or to compare their potential risks with conventional smoking cessation aids.
  - E-cigarettes simulate the cigarette smoking experience and may sometimes be used as cigarette cessation tool.
  - E-cigarettes still contain nicotine which is harmful to both mother and baby.
  - Nicotine has been associated with harm to the development of several organs. This includes lung function development, as well as impairment of the functions of the endocrine, reproductive, cardiovascular and neurological systems.
  - Evidence surrounding e-cigarettes in pregnancy is in its infancy.
  - There is no safe level of nicotine during pregnancy.
  - Studies indicate that e-cigarettes are unlikely to be risk-free in pregnancy.
  - McKee M, Capewell S. Evidence about electronic cigarettes: a foundation built on rock or sand? BMJ : British Medical Journal 2015;351.
  - McNeil A, Brose L, Calder R. E-cigarettes: an evidence update: a report commissioned by Public Health England. Public Health England. 2015.
  - Services UDoHaH. A Report of the Surgeon General: Highlights: Overview of Finding Regarding Reproductive Health. Atlanta US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health 2010.
  - Suter MA, Mastrobattista J, Sachs M, Aagaard K. Is There Evidence for Potential Harm of Electronic Cigarette Use in Pregnancy? Birth defects research Part A, Clinical and molecular teratology 2015;103:186-95.
  - Spindel ER, McEvoy CT. The Role of Nicotine in the Effects of Maternal Smoking during Pregnancy on Lung Development and Childhood Respiratory Disease. Implications for Dangers of E-Cigarettes. American Journal of Respiratory and Critical Care Medicine 2016;193:486-94.
  - Holbrook BD. The effects of nicotine on human fetal development. Birth Defects Research Part C: Embryo Today: Reviews 2016;108:181-92.
  - Coleman T, Chamberlain C, Davey M-A, Cooper SE, Leonardi-Bee J. Pharmacological interventions for promoting smoking cessation during pregnancy. Cochrane Database of Systematic Reviews 2015.
  - Vansickel AR, Cobb CO, Weaver MF, Eissenberg TE. A clinical laboratory model for evaluating the acute effects of electronic “cigarettes”: nicotine delivery profile and cardiovascular and subjective effects. Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology 2010;19:1945-53.
  - Bullen C, McRobbie H, Thornley S, Glover M, Lin R, Laugesen M. Effect of an electronic nicotine delivery device (e cigarette) on desire to smoke and withdrawal, user preferences and nicotine delivery: randomised cross-over trial. Tobacco Control 2010;19:98-103.
  - The Tobacco and Related Products Regulations 2016, Regulation 37. 2016. at http://www.legislation.gov.uk/uksi/2016/507/regulation/37/made.)
  - McGrath-Morrow SA, Hayashi M, Aherrera A, et al. The Effects of Electronic Cigarette Emissions on Systemic Cotinine Levels, Weight and Postnatal Lung Growth in Neonatal Mice. PLoS ONE 2015;10:e0118344.