Methods	Cluster-randomised trial of intervention to support women to stop smoking and prevent relapse in pregnancy and postpartum Study conducted in the Lodz district, Poland, with data collection from December 2000 to December 2001
Participants	Unit of randomisation was maternity units, selected from 33 in district and stratified by size. Control = 1 small, 2 medium, 2 big; Intervention = 2 small, 4 medium, 4 big (as higher refusal expected in intervention arms Inclusion criteria: Current smokers or women who quit 1 month before the visit Exclusion criteria: Not further specified. Recruitment: 15/33 maternity units were allocated to intervention (10) or control (5) groups All pregnant women screened. 194/194 (100%) eligible women in control group and 216/275 (78.5%) eligible women in the intervention group agreed to participate Baseline characteristics: Current smokers: C = 156, I = 158. Spontaneous quitters: C = 38, I = 58. Cigarettes per day: < 5 (C = 8.8%, I = 10.3%), 5-50 (C = 54.7%, I = 46%), > 10 (C = 36.5%, I = 43.7%). Fagerstrom score 0-6 (C = 98.9%, I = 92.3%) Mean age: C = 25.9, I = 25.5; < 12 years education: C = 76.2%, I = 74.3%; Unmarried: C = 39.2%, I = 52.5% Progress+ coding: Low SES population as described by author.
Interventions	Control: Received standard written information about health risks of smoking Intervention: Received 4-9 midwife home visits, based on a booklet translated from English (Ottawa) to Polish and adapted to Polish conditions: “How to talk about smoking with high risk pregnant smokers” Main intervention strategy: Counselling (single intervention) compared to usual care. Intensity: Frequency (C = 0, I = 6), Duration (C = 0, I = 4). Usual care intensity: F = 1, D=1 Intervention provided by midwives, which appear to be existing staff, though this is not explicitly reported: coded as effectiveness study
Outcomes	Self-reported smoking cessation ‘shortly after delivery at home’ (0-5 months postpartum*) Relapse prevention rates* in text (p274). Mean birthweight* calculated by combined smokers and quitters in Table 6 An associated reference (Polanska 2005) reports relapse after 12 months* (12-17 months postpartum). All randomised from women from original study included as denominator and those not included in the follow-up analysis assumed to have relapsed in this review. Spontaneous quitters and smokers combined from Table 2 to calculate self-reported abstinence at 12 months
Notes	No estimates of clustering effect reported, so sensitivity analysis conducted and intra-cluster correlation of 0.10 used to adjust data for inclusion in outcome tables as shown in Table 2.
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Notes random allocation, but no description of how this occurred. Only 15/33 eligible clinics allocated
Allocation concealment (selection bias)	Unclear risk	Not specified.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Attrition: Miscarriages: Smokers: I = 9/158 and C= 12/156. Spontaneous quitters: I = 2/58 and C= 1/38. Not included in analysis Those lost to follow-up: Smokers: (C = 6, I = 6) and Spontaneous quitters (C = 0, I = 2) are included in analysis of smoking outcomes
Selective reporting (reporting bias)	Unclear risk	Birthweight and relapse prevention outcomes difficult to interpret and unable to be included
Other bias	Unclear risk	Twice as many sites were allocated to the intervention arms as the control arms as it was assumed more women would refuse to participate in intervention activities. However recruitment to study arms was equal
Biochemical validation of smoking abstinence (detection bias)	High risk	Self-reported smoking status only.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Participants and personnel not blinded to this educational intervention
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete implementation	Unclear risk	No. of visits received not reported.
Equal baseline characteristics in study arms	High risk	Intervention group more likely to be married, have fewer children, and have a higher smoking addiction
Contamination of control group	Unclear risk	Cluster-design to minimise risk of contamination.