AIMS The aim of this study was to examine the safety of e-cigarettes (EC) and nicotine patches (NRT) when used to help pregnant smokers quit.

DESIGN A recent trial of EC versus NRT reported safety outcomes in the randomized arms. We conducted a further analysis based on product use.

SETTING Twenty-three hospitals in England and a stop-smoking service in Scotland took part.

PARTICIPANTS The participants comprised 1140 pregnant smokers.

INTERVENTIONS We compared women using and not using EC and NRT regularly during pregnancy.

MEASUREMENTS Measurements included nicotine intake compared with baseline, birth weight, other pregnancy outcomes, adverse events, maternal respiratory symptoms and relapse in early abstainers.

FINDINGS Use of EC was more common than use of NRT (47.3% vs 21.6%, P < 0.001). Women who stopped smoking (abstainers) and used EC at the end-of-pregnancy (EOP) reduced their salivary cotinine by 45% [49.3 ng/ml, 95% confidence interval (CI) = -79.8 to -10]. Only one abstainer used NRT at EOP. In dual users, cotinine increased by 19% (24 ng/ml, 95% CI = 3.5-68). In women reporting a reduction of at least 50% in cigarette consumption, cotinine levels increased by 10% in those using nicotine products and by 9% in those who did not. Birth weights in dual users and exclusive smokers were the same (3.1 kg). Birth weight in abstainers using either nicotine product was higher than in smokers [3.3 kg, standard deviation (SD) = 0.7] versus 3.1 kg, SD = 0.6; difference = 0.15 kg, 95% CI = 0.05-0.25) and not different from abstainers not using nicotine products (3.1 kg, SD = 0.8). Abstainers and smokers using nicotine products had no worse pregnancy outcomes or more adverse events than abstainers and smokers not using them. EC users reported more improvements than non-users in cough [adjusted relative risk (aRR) = 0.59, 95% CI = 0.37-0.93] and phlegm (aRR = 0.53, 95% CI = 0.31-0.92), controlling for smoking status. EC or NRT use had no association with relapse.

CONCLUSIONS Regular use of e-cigarettes or nicotine patches by pregnant smokers does not appear to be associated with any adverse outcomes.