Methods	Randomised controlled trial of telephone peer support to help women stop smoking in pregnancy Study conducted in a large obstetric practice in Burlington, Vermont (USA), with recruitment from 1996 to 1997
Participants	Inclusion criteria: Women reporting smoking at least 1 cigarette in the past week at their first antenatal visit Exclusion criteria: Not further specified. Recruitment: 151/186 (81%) women approached agreed to participate and were randomised (C = 74, I = 77) Baseline characteristics: Mean cigarettes/day before pregnancy: C = 20.2, I = 22.6; Mean cigarettes per day at first visit: C = 9.8, I = 10.5. Mean exhaled CO: C = 11.3, I = 11.3. Mean other smokers in household: C = 1.5, I = 1.3 Mean age C = 23.7, I = 23.1; Mean years education: C = 11.5, I = 11.7; White: C = 96%, I = 94.8%. Medicaid recipient: C = 74.6%, C = 77.5% Progress+ coding: Low SES.
Interventions	Control: Received brief smoking cessation advice (including encouraging a quit date) from a midwife or obstetrician at each of the 3 prenatal visits and stage appropriate printed materials. Midwives and obstetricians were provided with a 45 minute training session and protocol prompt sheets were placed in charts at first prenatal visits Intervention: Received the same as the control group, plus any women in the experimental visit who reported they possibly, probably or definitely intended to quit smoking were offered telephone peer support by the obstetrician/midwife. The telephone peer support was provided by a female ex-smoker, who received 8 hours of training. The support person called the participant within several days of referral to provide support, encouragement and reinforcement of positive changes in smoking behaviour. Ongoing calls typically occurred on a weekly basis, but more frequently around a quit date. On average calls lasted 10 minutes Main intervention strategy: Social support (tailored intervention) compared to a less intensive intervention Intensity: Frequency: (C = 3, I = 6), Duration (C = 1, I = 4). Unclear whether intervention provided by dedicated or existing staff
Outcomes	Biochemically validated 7-day point prevalence abstinence at 28-34/40 gestation (late pregnancy*) Proportion of smoking reduction by more than 50%* was reported for a proportion (135 women) but unclear how many had dropped out of intervention and control groups. As report states ‘no significant difference’ in dropouts by intervention group (total n = 16) we have imputed 8 for each arm and calculated the number of reductions from a proportion of the remaining sample Movement in stages of change also reported for this group.
Notes
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	States participants were randomised into either experimental or control condition
Allocation concealment (selection bias)	Unclear risk	No information.
Incomplete outcome data (attrition bias) All outcomes	Low risk	16/151 (11%) attrition at follow-up. Unclear how many from each arm, so outcomes (> 50% reduction and SOC movement) reported as a proportion of those remaining were not able to be included. All randomised women were included in the primary outcome of smoking cessation, with those lost to follow-up treated as continuing smokers
Selective reporting (reporting bias)	Unclear risk	Only smoking outcomes reported.
Other bias	Low risk	No other bias detected.
Biochemical validation of smoking abstinence (detection bias)	Low risk	Urinary cotinine assessment at 28-34 weeks used to confirm smoking status (cut-off <80 ng/mL)
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not feasible to blind participants and personnel to allocation. Medical charts flagged and referral for social support required by care providers
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete implementation	High risk	Process evaluation showed 53% received the peer intervention. 9 (12%) had low intentions of quitting smoking during pregnancy and were never offered the peer support, 9 (12%) had no home telephone and were not referred, and 15 (19%) refused the offering, leaving 44 (57%) who were referred for peer support. Data from log sheets completed by the telephone support person revealed that 3 women referred were never reached; therefore, only 53% of the women in the experimental condition received the peer support intervention
Equal baseline characteristics in study arms	Low risk	Baseline comparisons of women in the experimental and control conditions revealed no significant differences in demographics, pregnancy history, or smoking information
Contamination of control group	Low risk	Unlikely telephone counselling would have been provided to control group in error