Methods	3-armed randomised control trial of an intervention to support women to stop smoking and prevent relapse in pregnancy and postpartum The study was conducted at the Group Health Cooperative of Puget Sound (Seattle, USA) (HMO), and Park-Nicollet of Minnesota (USA), a multispecialty group practice. Years of data collection not stated
Participants	Inclusion criteria: Women who had completed the baseline survey, were < 20 weeks of pregnancy, were currently smoking or had smoked in the 30 days before pregnancy but had quit at the time of the baseline survey Exclusion criteria: Unable to speak English. Recruitment: Women booked for a first prenatal visit were offered, by letter, study participation and unless they opted out were given a baseline telephone interview to assess smoking status. 9152 approached, 714 ineligible because of miscarriage, pregnancy termination, inability to speak English; 697 (8%) refused; 262 could not be reached by telephone after repeated attempts. 7479 (82%) completed survey. 1007/7479 (13%) were current smokers or recent quitters and were randomised: 897 participated (457 from Seattle, 440 from Minnesota), C = 297, I1 = 294, I2 = 306. Current smoker at baseline = 56% (C = 165, I1 = 176, I2 = 160). Baseline characteristics: Mean cigarettes/day before pregnancy = 14.9; Current mean cigarettes/day = 4.8. Mean age 27.7 years; Household income >= 30000 $US 67%; College graduates 17%; 88% white Progress+ coding: None.
Interventions	There were 3 stages of change based interventions, all delivered by mail or telephone without involving prenatal care providers. Control: Self-help booklet “Stop now for your baby”; 5th grade reading level; health effects of smoking during pregnancy; specific suggestions for quitting (setting date, enlisting support). For recent quitters: stress reduction techniques; suggestions for handling high-risk situations; pregnancy-appropriate behavioural alternatives to smoking. Intervention 1: High intensity interventions in pre and postpartum groups also received: (i) a personalised letter acknowledging baseline readiness for change, personal health concerns, motivation to quit, comparison with other pregnant women who had successfully quit. (ii) relapse prevention kit within 2 weeks of completing the 28 week follow-up survey. (iii) a booklet which discussed transition from pregnancy and factors that influence cessation and relapse; practical tips for high-risk situations, strategies for avoiding self-defeating reactions to slips, personal anecdotes from women who quit. (iv) 3 antenatal counselling phone calls: 2 weeks after the booklet and 1 and 2 months later. Calls were open-ended but with standardised protocol based on motivational interviewing and with stage-based objectives average 8.5 min. Intervention 2: The pre-post group received as for group 2 + an additional 3 counselling calls in the first 4 months after birth reinforcing themes from the Relapse Prevention booklet; 3 newsletters at 2, 6 and 12 months postpartum about health effects of environmental tobacco smoke and the importance of being a non-smoking parent Main intervention strategy: Counselling (multiple intervention) compared to less intensive intervention. Intervention 1 and 2 were only reported as combined outcomes in late pregnancy, and included in this review. Postpartum outcomes are reported by intervention group and combines smokers at baseline and spontaneous quitters Intensity: Frequency (C = 2, I = 6); Duration (C = 1, I = 3). Intervention provided by dedicated project staff: Efficacy study
Outcomes	Self-reported 7-day point prevalence abstinence at 28 weeks’ gestation (late pregnancy*), with sample biochemically validated. (combined I1&I2); Relapse prevention in late pregnancy (spontaneous quitters*); Abstinence at 8 weeks (0-5 months*); 6 months* (6-11 months); and 12 months (12-17 months) postpartum (combined baseline smokers and spontaneous quitters). Response rates were 92% at 28 weeks; 91% at 8 weeks’ postpartum; 89% at 6 months postpartum; 87% at 12 months postpartum A subsequent paper reports partner abstinence.
Notes	Process evaluation describes participation in specific intervention components, including relapse prevention
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described. They were stratified by baseline smoking status
Allocation concealment (selection bias)	Unclear risk	No information provided.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	110/1007 (11%) attrition. 88 miscarried and 22 were sent wrong intervention material and were excluded from analysis. 897 women included in final analysis. For self-reported smoking status non-respondents were treated as continuing smokers
Selective reporting (reporting bias)	Unclear risk	Smoking outcomes only reported and only combined outcomes for abstinence at 28 weeks’ gestation
Other bias	Low risk	No other bias detected.
Biochemical validation of smoking abstinence (detection bias)	High risk	Salivary cotinine analysis. Salivary cotinine requested from all who reported abstaining for 7 days (< 20 ng/mL as cut-off). 64%-78% returned saliva samples and as there were no differences, outcomes reported are based on self-reported status
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not feasible to blind providers and women to counselling intervention
Blinding of outcome assessment (detection bias) All outcomes	Low risk	All samples were analysed for cotinine at the American Health Foundation laboratory. The computer-assisted telephone surveys were implemented by trained interviewers who had no role in intervention activities
Incomplete implementation	Low risk	Over 90% in the intervention group recalled receiving the self-help booklet, relapse prevention kit, counselling calls and newsletters
Equal baseline characteristics in study arms	Unclear risk	There were some baseline differences reported in text.
Contamination of control group	Low risk	The intervention was delivered via mail and telephone without involving prenatal health care providers