Methods	Cluster-randomised trial of smoking cessation in public prenatal and WIC clinics in Maryland, Colorado and Missouri, USA, 1987-89
Participants	5262, 6087 and 4943 pregnant women screened in Colorado, Missouri and Maryland respectively, with nearly 50% of women in each State smoking. Smoking defined as “even a puff within the last 7 days before the women knew she was pregnant” (includes recent quitters). Consent for data collection ranged from 66% to 79%. High proportions were young, <12 years education, White, unmarried and poor. Mean gestation at enrolment = 15.2 - 16.6 weeks. Mean cigarettes/day at enrolment combined for smokers = 12 cigarettes/day
Interventions	Control: UC not otherwise specified by usual clinic staff. Interventions based on stages of change, but differed by State, locally adapted with some detailed development. Colorado: 1-5 minutes counselling; assessing smoking status; quitting tips; supportive statements by nurse-clinicians; healthcare providers’ Guide; 8 brochures for pregnant smokers; additional one for women postpartum. Maryland: brief clinic-based counselling program + self-help material focussing on the stages of quitting. Missouri: “becoming a life-long smoker” 6 minutes with clinic patient brochures, flip charts; 1-2 minutes at WIC clinics training staff, chart documentation and forms. All included effects of smoking on the fetus; benefits of quitting; quitting techniques; developing social support; preventing relapse and limiting exposure to environmental tobacco smoke. All materials were at 6th Grade reading level. Intensity rating: I = 3, C = 1 (not clear and varied)
Outcomes	Smoking cessation biochemically validated with urine cotinine. The necessary adjustment for clustering means that the data cannot be put into the standard table of comparisons. Adjusted data showed no differences in verified quitting, mean birthweight or low birthweight
Notes	Intracluster correlation of 0.003 reported and used for adjusting outcome figures in analysis. Substantial misclassification of self-report as non-smoking: 28% at enrolment; 35% at 8th month; 49% of self-reported quitters at intervention clinics; 32% of self-reported quitters at control clinics. Process evaluation suggested less difference between I and C clinics than might have been expected. Project staff felt that the use of existing staff to deliver the new interventions and to collect data affected the study negatively especially given the time needed to process questionnaires and urine samples. This led to less than full implementation and variable motivation to promote smoking cessation counselling among staff
Risk of bias
Item	Authors’ judgement	Description
Adequate sequence generation?	Unclear	Clinics stratified by size of clinic and also by prior low birthweight programme (Colorado) or % minority clients (Maryland), and randomly assigned to deliver either intervention or continue with standard care. No details of randomisation provided
Allocation concealment?	Unclear	Cluster-randomised trial.
Blinding? Women and clinical staff	Unclear	Unclear whether participants and providers were aware of clinic allocation
Incomplete outcome data addressed? All outcomes	Unclear	Records used to collect some outcome data for respondents lost to follow up. Loss to follow up balanced in experimental and control groups. Varying enrolment and attrition rates in different centres. No ITT analysis
Free of selective reporting?	Unclear	High rates of non-disclosure for smoking outcomes.
Free of detection bias?	Yes	Biochemical validation by urinary cotinine.