Methods	Cluster-randomised controlled trial to support women to stop smoking and prevent relapse during pregnancy and postpartum Study conducted in public prenatal and WIC clinics in Maryland, Colorado and Missouri (USA), with data collection from 1987 to 1991
Participants	Inclusion criteria: Smoking defined as “even a puff within the last 7 days before the women knew she was pregnant”, who were aggregated into ‘enrolment smokers’ (smoked within 7 days before study enrolment) and ‘recent quitters (smoked before they thought they were pregnant) Exclusion criteria: Not further specified. Recruitment: 1741/5262, 1936/6087 and 1895/4943 pregnant women screened in Colorado, Missouri and Maryland respectively, with nearly 50% of women in each state smoking. Participation rates ranged from 66% in Maryland to 79% in Missouri Baseline characteristics: Mean cigarettes/day at enrolment combined for smokers = 12 cigarettes/day High proportions were young, < 12 years education, white, unmarried and poor. Mean gestation at enrolment = 15.2 - 16.6 weeks Progress+ coding: Low SES.
Interventions	Control: Usual care not otherwise specified by usual clinic staff. Intervention: 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 1 for women postpartum. Maryland: brief clinic-based counselling program + self-help material focusing on the stages of quitting. Missouri: “becoming a life-long smoker” six 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 Main intervention strategy: Counselling (multiple intervention) compared to usual care Intensity: Frequency (C = 0, I = 2), Duration (C = 0, I = 1). Usual care intensity: F = 0, D = 0 Intervention provided by existing staff: Effectiveness study
Outcomes	Biochemically validated point prevalence abstinence at 8 months gestation (late pregnancy*). Smoking outcomes for ‘recent quitters’ (relapse prevention) were not reported. Birthweight and proportion of low birthweight babies are not reported by intervention group so were unable to be included in meta-analysis
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
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	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 (selection bias)	Unclear risk	Cluster-randomised trial.
Incomplete outcome data (attrition bias) All outcomes	High risk	In the 3 states combined, the reasons for loss to follow-up at the eighth month were early termination of pregnancy (7. 6%); enrolment after 32 weeks (6.1%); lost, moved, or unable to locate (27.7%) ; referred to another care provider (2.8%); and refused data collection (1.0%). The total number of enrolment smokers were not reported by intervention groups, and attrition rates were not reported by intervention groups, so we were unable to re-include data for respondents lost to follow-up. Report states loss to follow-up was balanced in experimental and control groups. Varying enrolment and attrition rates in different centres. No ITT analysis
Selective reporting (reporting bias)	Unclear risk	High rates of non-disclosure for smoking outcomes.
Other bias	Unclear risk	Uneven recruitment to study arms in Maryland, which affected the overall allocation (C = 1767, I = 1467)
Biochemical validation of smoking abstinence (detection bias)	Low risk	Biochemical validation by urinary cotinine (< 85 ng/mL indicates active smoker)
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Unclear whether participants and providers were aware of clinic allocation
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete implementation	High risk	Process evaluation reported that implementation was less than ideal
Equal baseline characteristics in study arms	Low risk	Intervention and control sites were similar at enrolment, indicating that stratification and randomisation had been effective (data not shown)
Contamination of control group	Unclear risk	Many patients at control clinics also reported having received (non-SCIP) materials and counselling which indicated that usual care included exposure to smoking cessation messages