Methods	Randomised controlled trial of counselling intervention to support women to stop smoking and prevent relapse in pregnancy Study conducted in a large public antenatal clinic, in Rotunda Ireland, with recruitment during 3 months in 1995
Participants	Inclusion criteria: Women who ‘currently smoke’ or had spontaneously quit since becoming pregnant Exclusion criteria: Non-viable pregnancy identified at first visit or intending to deliver at another hospital Recruitment: 967/524 (54%) women attending the public clinic were smokers. 418/518 (81%) eligible women agreed to participate and were randomised (C = 209, I = 209) Baseline characteristics: Current smoker: C = 192, I = 203; Spontaneous quitter: C = 17, I = 6; 34% smoked more than 20 cigarettes per day currently; Partner smoking: C = 74%, I = 69.9% < 21 years age C = 17%, I = 24%; Mean gestation at first visit I = 15.5, C = 15.3; Not living with partner C = 39.2%, I = 42.6%; age finished education C = 16.1, I = 16.0; Lower social class C = 71.5%, I = 70.9% Progress+ coding: Low SES.
Interventions	Control: Routine prenatal advice on a range of health issues, from midwives and obstetricians Intervention: As for the control group + (i) structured 1 to 1 counselling by a trained facilitator (based on stages of change theory); (ii) partners invited to be involved in the program; (iii) an information pack (developed in collaboration with a focus group of women), which included a self-help booklet; (iv) and invited to join a stop smoking support group. A CO monitor was available for the intervention group, to quantify smoking habit and act as a motivational tool Main intervention strategy: Counselling (tailored) compared to usual care. Intensity: Frequency: (C = 0, I = 5); Duration (C = 0, I = 2). Usual care intensity: F = 1, D = 1 Intervention provided by dedicated study staff: Efficacy study
Outcomes	Biochemically validated smoking cessation* and relapse prevention* at delivery (late pregnancy) and 3 months postpartum among baseline smokers* and spontaneous quitter. Mean cigarettes per day at delivery*, reduction in daily cigarettes since first visit, quit attempts, comparisons of quitters and non quitters at various stages. Infant outcomes at birth (singleton births): mean birthweight*, proportion LBW(2500 g)*, preterm births*, stillbirths*, neonatal deaths*, NICU admissions*, delivery type, mean gestation Infant outcomes at 3 months postpartum: neonatal deaths, attendance at GP; attendance or admission to hospital
Notes	Detailed process analysis and participant feedback of program implementation
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Random number tables with restricted randomisation in groups of 10
Allocation concealment (selection bias)	Low risk	Sealed opaque envelopes.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	31/418 (7%) attrition at delivery (I = 13/209 or 6.2%, C 18/209 or = 8.6%). Miscarriage (7), delivered elsewhere (3), moved overseas (2), changed care provider (7) or never returned to Rotunda hospital after first visit (12), and were excluded from this analysis All other women lost to follow-up counted as continuing smokers in this review
Selective reporting (reporting bias)	Low risk	All outcomes reported.
Other bias	Low risk	No other bias detected.
Biochemical validation of smoking abstinence (detection bias)	Unclear risk	Exhaled CO measurement on 145/209 women on postnatal ward (cut-off < 4 ppm). Presume smoking outcomes reported are those biochemically validated although this is not explicitly stated
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not feasible to blind participants and study personnel to counselling intervention. Intervention provided by trained facilitator, with staff unaware of allocation
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete implementation	High risk	Detailed process evaluation describes how women rarely initiated contact at subsequent visits and the groups sessions were poorly attended
Equal baseline characteristics in study arms	High risk	Intervention group were less likely to have spontaneously quit, or be employed
Contamination of control group	Low risk	Research facilitator provided intervention.