Bauman 1983.

Methods	Randomised controlled trial of use of exhaled CO feedback for promoting smoking cessation in pregnancy. Study conducted in Guildford County, North Carolina, USA over 6 months in 1981.
Participants	Inclusion criteria: Women currently or recently smoking, attending public clinics. Exclusion criteria: Not reported. All women attending AN care‐orientation sessions were randomly allocated to experimental or control groups. Recruitment: 226 women entered prenatal program and 170 (75%) included in analyses. The authors compared those who did not participate and did not find any significant differences. 47% (79/170) were current smokers (C = 43, I = 36). Baseline characteristics: 43% had completed high school education, 56% were black, 80% classified as having no pregnancy risks other than smoking. 38% in the first trimester and 46% in the second trimester of pregnancy. Progress + coding: Low SES as all attending public prenatal clinic.
Interventions	Control: Women were read a 135 script that described the relationship among cigarette smoking, CO, and the harmful consequences of smoking. Intervention: Experimental group received same information as control group, and they provided breath specimen in which CO was measured, with feedback of the result. Main intervention strategy: Feedback (single intervention) compared to a less intensive intervention. Intensity: Frequency (C = 1, I = 1); Duration (C = 1, I = 1). Implemented by regular health educators: effectiveness study.
Outcomes	Biochemically validated abstinence 6 weeks after intervention (late pregnancy*). Exhaled CO (ppm), but no SD reported; unclear if 'quantity of cigarettes' is mean cigarettes per day; how recent was smoking; depth of inhalation.
Notes	Not clear whether this was a group intervention ‐ in which case there was no adjustment for clustering.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Random number table.
Allocation concealment (selection bias)	Unclear risk	No information provided.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Unclear exactly how many women were randomised to each group, however we assume that those reported as 'current smokers' in table 1 are the baseline numbers, which were all included in this review.
Selective reporting (reporting bias)	Unclear risk	None apparent.
Other bias	Low risk	No other bias detected.
Biochemical validation of smoking abstinence (detection bias)	Low risk	Biochemical validation of reported smoking behaviour for those followed up (CO >= 9 ppm in exhaled air).
Blinding of participants and personnel (performance bias) All outcomes	High risk	Intervention was carried out by clinical staff, no participant blinding reported.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete implementation	Low risk	All women apparently received the intervention.
Equal baseline characteristics in study arms	Low risk	No difference between experimental and control arms on 12 variables measured.
Contamination of control group	Low risk	Implemented by regular health educators at the maternity clinics.