Copyright © The British Psychological Society Reproduction in any form (including the internet) is prohibited without prior permission from the Society A randomized controlled trial of smoking cessation for pregnant women to test the effect of a transtheoretical model-based intervention on movement in stage and interaction with baseline stage Paul Aveyard*, Terry Lawrence, K. K. Cheng, Carl Griffin, Emma Croghan and Carol Johnson Department of Public Health and Epidemiology, University of Birmingham, UK Objectives. To examine whether, as predicted by the transtheoretical model (TTM), stage-matched interventions will be more effective than stage-mismatched interventions. Design. Randomized controlled trial of smoking cessation advice to pregnant smokers. Methods. Pregnant women currently smoking at 12 weeks gestation were enrolled in a pragmatic three-arm trial of TTM-based interventions to help them stop smoking. One arm constituted standard midwifery advice and a self-help leaflet on stopping smoking, which is generally appropriate for women in preparation. Two arms were TTM-based. Differences in positive movement in stage towards quitting from enrolment to 30 weeks gestation and 10 days post-partum were calculated for each arm of the trial. We then examined whether, as predicted from the TTM, the relative benefit of the TTM-based intervention was greater for women in precontemplation and contemplation, for whom the control intervention was stage-mismatched, than for women in preparation, for whom the control intervention was stage-matched. Results. Women in the TTM-based arms were statistically significantly more likely to move forward in stage than were women in the control arm. Contrary to the TTM- derived hypothesis, the greater relative benefit of the TTM-based intervention was seen for women in preparation stage at baseline, rather than women in precontemplation and contemplation. Conclusions. The TTM-based intervention was more effective in stage movement, but this could be due to its greater intensity. The failure to confirm that stage-matching was important casts doubt on the validity of the TTM in explaining smoking cessation behaviour in pregnancy. * Correspondence should be addressed to Paul Aveyard, Department of Primary Care, University of Birmingham, Birmingham B15 2TT, UK (e-mail: p.n.aveyard@bham.ac.uk). The British Psychological Society 263 British Journal of Health Psychology (2006), 11, 263–278 q 2006 The British Psychological Society www.bpsjournals.co.uk DOI:10.1348/135910705X52534