Methods	Cluster-randomised trial of self-help booklets to support women to stop smoking and prevent relapse in pregnancy Study conducted in 3 NHS hospital trusts in England (UK), with recruitment from May 1998 to July 2000
Participants	Inclusion criteria: Midwives were the unit of randomisation. Women attending first visit; >= 16 years; < 17 weeks’ gestation; literate in English were eligible. Smokers counted as those who reported “I smoke now”, “I smoke now but have cut down since I thought I might be pregnant”, or “I have stopped smoking since I thought I might be pregnant” Exclusion criteria: Not further specified. Recruitment: All 128 community midwives in 3 trusts agreed to participate and were randomly allocated to 6 strata (C = 64, I = 64). Three midwives went on maternity leave and did not recruit any women (C = 64, I = 61). 8,586 women screened and 1527/1803 (85%) eligible women consented to participate (C = 803, I = 724) Baseline characteristics: Current smokers: C = 97, I = 97; Current but reduced since pregnancy: C = 464, I = 445 (All current smokers C = 561, I = 542); Recent quitters: C = 242, I = 182. Mean cigarettes per day before pregnancy: C = 15.1, I = 16. Mean cigarettes per day at baseline C = 5.5, I = 6.4 Maternal age: C = 26.7, I = 27.2. Left full time education by 16 years: C = 63.6%, I = 61%. Progress+ coding: Low SES.
Interventions	Control: Midwives continued to give routine advice according to usual practice. Intervention: Midwives spent at least 5 minutes introducing a series of 5 self-help booklets “Stop for Good”, based on stages of change theory, and gave them a copy of the first booklet. Subsequent booklets were mailed directly to the woman Main intervention strategy: Counselling (single intervention) compared to usual care. Intensity: Frequency: (C = 0, I = 4), Duration (C = 0, I = 1). Usual care intensity: F = 1, D = 1 Intervention provided by existing staff: Effectiveness study
Outcomes	7-day point prevalence abstinence at 26 weeks’ gestation (late pregnancy*), with 94% validated by urine cotinine (80 ng/mL). Self-reported mean cigarettes per day in late pregnancy*. Relapse prevention for recent quitters not reported separately so outcomes for smokers and recent quitters are combined in this analysis. Stillbirths or neonatal deaths (not included as unable to separate), and preterm births (< 27 weeks) not included as rates < 36-37 weeks not reported. Reported as ‘attrition’
Notes	Reported intracluster correlation of 0.031 used to adjust outcome data for inclusion in outcome tables. Sample size justification
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Stratified random allocation by computer-generated random numbers. 118 midwives stratified according to workload and randomly allocated to provide intervention or control care
Allocation concealment (selection bias)	Unclear risk	No information.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	92/1527 (6%) excluded from analysis due to miscarriage or termination (C = 36, I = 40), stillbirth or neonatal death (C = 9, I = 6)-not included as unable to separate, preterm birth (C = 1). Those lost to further follow-up (C = 50, I = 68) were included as continuing smokers in this review, leaving 1435 (C = 757, I = 678)
Selective reporting (reporting bias)	High risk	Outcomes not reported separately for baseline smokers and spontaneous quitters
Other bias	Unclear risk	Some unequal recruitment in each arm
Biochemical validation of smoking abstinence (detection bias)	Low risk	Urinary cotinine levels analysed (cut-off 60 ng/mL and 100 ng/mL)
Blinding of participants and personnel (performance bias) All outcomes	High risk	Midwives randomised. Educational intervention.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Outcome assessment blinding not reported. However, follow-up rates were high in both groups, and all data coding and cleaning was undertaken blind to treatment allocation
Incomplete implementation	High risk	Detailed qualitative and quantitative process analysis of participants’ and midwives’ views of the intervention, which suggested poor implementation in some areas
Equal baseline characteristics in study arms	High risk	There were some differences between the 2 treatment groups at baseline, most notably in the numbers of women who had stopped smoking before the booking appointment and in the quantity of cigarettes consumed before the pregnancy and at the time of booking
Contamination of control group	High risk	Some concerns about contamination of control group reported.