Comparison of saliva cotinine and exhaled carbon monoxide concentrations when smoking and after being offered dual nicotine replacement therapy in pregnancy

BACKGROUND AND AIMS: Although English Stop Smoking Services routinely offer dual nicotine replacement therapy (NRT) to help pregnant women to quit smoking, little is known about how nicotine and tobacco smoke exposures following this compare with that from smoking. We compared, in pregnant women when smoking and after being offered dual NRT, saliva cotinine and exhaled carbon monoxide (CO) concentrations and numbers of daily cigarettes smoked. DESIGN AND SETTING: Secondary analysis of data from three sequential, observational, mixed‐methods cohort studies conducted as part of the Nicotine Replacement Effectiveness and Delivery in Pregnancy programme. Participants were recruited on‐line or in Nottingham University Hospitals (UK) antenatal clinics between June 2019 and September 2020. PARTICIPANTS: Forty pregnant women, who agreed to try stopping smoking. INTERVENTION: Participants were offered dual NRT, agreed a smoking quit date and received an intervention to improve adherence to NRT. MEASUREMENTS: Saliva cotinine and exhaled CO concentrations and reported number of cigarettes smoked per day. FINDINGS: There were no differences in saliva cotinine concentrations at baseline and day 7 post quit date [n = 20, mean difference = −32.31 ng/ml, 95% confidence interval (CI) = −68.11 to 3.5 ng/ml; P = 0.074, Bayes factor = 0.04]. There were reductions in the reported number of cigarettes smoked per day (n = 26, mean difference = −7 cigarettes, 95% CI = −8.35 to −5.42 cigarettes, P < 0.001) and concurrently in exhaled CO concentrations (n = 17, ratio of geometric means = 0.30 p.p.m., 95% CI = 0.17–0.52 p.p.m.; P < 0.001). CONCLUSION: Pregnant women who smoke and are offered dual nicotine replacement therapy (NRT) appear to show no change in their exposure to cotinine compared with their pre‐NRT exposure levels but they report smoking fewer cigarettes, as validated by reductions in exhaled carbon monoxide concentrations.