The relationship between reported daily nicotine dose from NRT and daily cigarette consumption in pregnant women who smoke in an observational cohort study

Introduction For non-pregnant people unable to quit smoking, the NHS recommends nicotine replacement therapy (NRT) for smoking reduction. This is not recommended during pregnancy due to concerns about higher nicotine intake than smoking alone. We investigated the relationship between daily nicotine dose from NRT and cigarette consumption reported by pregnant women receiving smoking cessation support. Methods We conducted secondary analysis of data from currently smoking pregnant women, recruited from antenatal clinics (Nottingham University Hospitals, UK) or online between June 2019-September 2020. Participants set a quit date, received a prototype NRT adherence intervention, and reported cigarettes per day (CPD) and daily NRT dose (mg) via smartphone app for 28 days. Results 388 women were screened, 32 (8%) were eligible and joined the study. 24 (75%) submitted 510 app reports in total. 17 (71%) reported smoking and using NRT concurrently on at least one day, with concurrent use reported on 109 (21%) of app reports. The relationship between daily NRT dose and CPD followed an exponential decay curve of approximately 7%. In multilevel repeated measures modelling using 4 linear splines (knots 17, 40 and 85 mg/NRT), significant fixed effects of daily NRT dose on CPD were observed for splines 1, 3 and 4. The strongest association was spline 1 (0-17 mg/NRT), where each 10mg NRT increase was associated with a 0.6 CPD reduction (24% on average). Conclusions Among women in a cessation study, many smoked and used NRT concurrently; within these women, daily nicotine dose and heaviness of smoking were inversely related. Implications Findings have implications for the design of future interventions intended to reduce harm associated with smoking in pregnancy. They suggest using NRT alongside smoking in pregnancy could help some women reduce the number of cigarettes they smoke per day