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Published: 17 January 2024

New analysis of trial data on pregnant smokers finds that the regular use of nicotine replacement products during pregnancy is not associated with adverse pregnancy events or poor pregnancy outcomes.

The PREP 2 study, funded by the National Institute for Health and Care Research (NIHR), used data collected from over 1,100 pregnant smokers attending 23 hospitals in England and one stop-smoking service in Scotland. They compared the pregnancy outcomes in these women who did or did not use nicotine in the form of e-cigarettes or nicotine patches regularly during their pregnancy.

Researchers took measurements of salivary cotinine levels at the start of the study and towards the end of pregnancy. They gathered information about each participant’s use of cigarettes or types of nicotine replacement therapy, any respiratory symptoms, birth weight and a range of other data from their babies at birth.

Nicotine containing aids to stop smoking in pregnancy appears safe

The study, published today in the journal Addiction, found that e-cigarettes were more commonly used in the group than nicotine patches (47% compared with 21%), and that regular use of these nicotine products was not associated with any adverse effects in the mothers or their babies.

Women who smoked and used one of the nicotine replacement products during their pregnancy gave birth to babies with the same birth weights as women who only smoked. Babies born to women who did not smoke during pregnancy did not differ in birth weight, whether the women did or did not use nicotine products.

The results also confirmed previous unexpected findings that e-cigarette use may reduce respiratory infections in vapers, possibly because the main ingredients of e-cigarettes - aerosol, propylene glycol, and glycerine - have antibacterial effects.

Good news for those making vital steps to stop smoking

“This study is important as it shows that individuals who stop smoking early in their pregnancy and switch to vaping or using nicotine replacement therapy are no more likely to have poor pregnancy and birth outcomes, such as low birth weight, than those who stopped smoking without using these nicotine products. This is good news for pregnant women who are making vital steps to stop smoking.

- Professor Michael Ussher from the Population Health Research Institute at St George’s, University of London, who was involved in the study -

Professor Michael Ussher added: "This work provides the most reliable evidence as it more carefully measured the levels of use of nicotine products and smoking than previous studies. The problem with any earlier studies reporting harm of vaping in pregnancy is that this could be due to current or previous smoking.”

Professor Peter Hajek from Queen Mary University of London, who led the research, said: "The trial contributes answers to two important questions, one practical and one concerning our understanding of risks of smoking. E-cigarettes helped pregnant smokers quit without posing any detectable risks to pregnancy compared with stopping smoking without further nicotine use. Using nicotine containing aids to stop smoking in pregnancy thus appears safe. The harms to pregnancy from smoking, in late pregnancy at least, seem to be due to other chemicals in tobacco smoke rather than nicotine."

Learn more about research at St George's Population Health Research Institute

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