The cessation in pregnancy incentives trial (CPIT): study protocol for a randomized controlled trial

Abstract

Background: Seventy percent of women in Scotland have at least one baby, making pregnancy an opportunity to help most young women quit smoking before their own health is irreparably compromised. By quitting during pregnancy their infants will be protected from miscarriage and still birth as well as low birth weight, asthma, attention deficit disorder and adult cardiovascular disease. In the UK, the NICE guidelines: 'How to stop smoking in pregnancy and following childbirth' (June 2010) highlighted that little evidence exists in the literature to confirm the efficacy of financial incentives to help pregnant smokers to quit. Its first research recommendation was to determine: Within a UK context, are incentives an acceptable, effective and cost-effective way to help pregnant women who smoke to quit?

Design and methods: This study is a phase II exploratory individually randomized controlled trial comparing standard care for pregnant smokers with standard care plus the additional offer of financial voucher incentives to engage with specialist cessation services and/or to quit smoking during pregnancy.Participants (n = 600) will be pregnant smokers identified at maternity booking who, when contacted by specialist cessation services, agree to having their details passed to the NHS Smokefree Pregnancy Study Helpline to discuss the trial. The NHS Smokefree Pregnancy Study Helpline will be responsible for telephone consent and follow-up in late pregnancy. The primary outcome will be self reported smoking in late pregnancy verified by cotinine measurement. An economic evaluation will refine cost data collection and assess potential cost-effectiveness while qualitative research interviews with clients and health professionals will assess the level of acceptance of this form of incentive payment. The research questions are: What is the likely therapeutic efficacy? Are incentives potentially cost-effective? Is individual randomization an efficient trial design without introducing outcome bias? Can incentives be introduced in a way that is feasible and acceptable?

Discussion: This phase II trial will establish a workable design to reduce the risks associated with a future definitive phase III multicenter randomized controlled trial and establish a framework to assess the costs and benefits of financial incentives to help pregnant smokers to quit.

Trial registration: Current Controlled Trials ISRCTN87508788.

Figure 1

Funnel plot. Figure 1 is a funnel plot of all studies included in the Cochrane systematic review: interventions for promoting smoking cessation during pregnancy [10]. The overall risk ratio for smoking cessation in each study is plotted on the x axis. The sample size of each study is plotted on the y axis. The plot illustrates possible publication bias with a gap caused by ‘missing’ studies upsetting the symmetry on the right hand side of the figure, indicating that small negative studies may not have reached the point of publication. Diamond shaped symbols indicate individual randomization whereas square symbols indicate that cluster randomization was used in the trial. The four black diamond shapes on the left side represent the four incentives trials included in the review. The dashed vertical line crosses the x axis at the weighted mean risk ratio of smoking reduction in all studies comparing intervention with control – 0.94 (95 % confidence interval 0.93 to 0.95).

Figure 2

Flow diagram for Cessation in Pregnancy Incentives Trial (CPIT). Figure 2 projects the flow of pregnant women through the trial over a 12-month period. In the NHS Greater Glasgow & Clyde study area, 15,000 pregnancies are recorded at maternity booking; 5,000 are to smokers, some who conceal their habit, and 3,000 are identified at maternity booking by self-report as current smokers. Their information is routinely passed to NHS Smokefree Pregnancy Services (NSPS) using an automated system. Attempt is made to contact all self reported smokers. We estimate that 500 will not be contactable by NSPS and that 500 will decline permission for their details to be passed to the NHS Smokefree Pregnancy Study Helpline (Study Helpline). Once details have been passed, 500 will not be contactable leaving 1,500 contacted by the Study Helpline. We expect that 600 to 900 will decline consent leaving 600 to 900 who agree to enroll in the study over 12 months. Of these, 300 will be randomly allocated to the intervention group to be offered incentive payments as well as standard care to stop smoking during pregnancy and 300 will be randomly allocated to receive the offer of standard care without incentive payments to quit smoking.