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. 2017 Feb 14;2017(2):CD001055. doi: 10.1002/14651858.CD001055.pub5

Heil 2008.

Methods Randomised controlled trial of financial incentives to support women to stop smoking in pregnancy and prevent relapse postpartum.
Study conducted in Greater Burlington, Vermont (USA) with data collection from 2001 to 2003.
Participants Inclusion criteria: Self‐reported smoking (even a puff in the last 7 days), gestational age less than 20 weeks, living within study clinic county and not planning to move until at least 6 months postpartum, and speaks English.
Exclusion criteria: Incarceration or previous participation in the study or living with anyone who has previously participated in the study.
Recruitment: Participants were recruited from 1 of 4 large obstetric practices in the Women, Infants and Children (WIC) program. 182 women were eligible for the study, and 82 (45%) agreed to participate. Mean gestation at recruitment (I = 8.9, C = 9.5). 77 included in analysis (C = 40, I = 37).
Baseline characteristics: Pre‐pregnancy cigarettes per day (I = 18.7, C = 18.4),
Health insurance (I = 19%, C = 13%).
Progress + coding: Low SES as WIC program recipients.
Interventions Control (non‐contingent voucher): Participants received voucher independent of smoking status. US$ 15.00 per AN visit and US$ 20.00 per postpartum visit, to result in comparable average earnings to the contingent group. Both groups received routine advice from the clinic.
Intervention (contingent voucher): participants chose a quit date, and reported daily to the clinic for CO monitoring for 5 days, then urine cotinine monitoring twice weekly for 7 weeks, weekly for 4 weeks, and then every 2 weeks for the remainder of the pregnancy. Vouchers were given dependent on biochemical validation, beginning at US$ 6.25 and escalated by US$ 1.25 to a maximum of US$ 45.00. Positive test results reset voucher back to original value, but 2 consecutive negative tests restored value to pre‐reset value. It is unclear who delivered the intervention.
Main intervention strategy: Incentives (single intervention) compared to alternative intervention.
Intensity: Frequency (C = 6, I = 6), Duration (C = 6, I = 6).
Intervention provided by study staff: efficacy study.
Outcomes Biochemically validated smoking cessation (7‐day point prevalence) at >= 28 weeks' gestation (late pregnancy*), 12 weeks (0‐5 months*) and 24 weeks' (6‐11 months*) postpartum. Reduction in mean cotinine.
Mean birthweight*, gestational age, fetal growth measures (US), and proportion of NICU admissions, LBW* infants, and preterm births*.
Nicotine withdrawal symptoms reported in associated reference (Heil 2004).
Notes Sample size justification. Some discussion of cost implications.
Risk of bias
Bias Authors' judgement Support for judgement
Random sequence generation (selection bias) Unclear risk Described as "randomisation stratified to clinics". Details of randomisation not described.
Allocation concealment (selection bias) Unclear risk No information.
Incomplete outcome data (attrition bias) 
 All outcomes Unclear risk 5 women withdrew from the study due to fetal demise or termination of pregnancy and were not included in the final analysis (I = 3, C = 2).
Selective reporting (reporting bias) Low risk Detailed birth outcomes reported.
Other bias Low risk No other bias detected.
Biochemical validation of smoking abstinence (detection bias) Low risk Biochemical validation using exhaled CO for 5 days (< 6 ppm) and then urine cotinine (< 80 ng/mL) after 2 weeks.
Blinding of participants and personnel (performance bias) 
 All outcomes High risk Participants and providers not blinded as receiving incentives for participation.
Blinding of outcome assessment (detection bias) 
 All outcomes Unclear risk Not reported.
Incomplete implementation Low risk Compliance with periodic assessments was relatively high (83%–95%).
Equal baseline characteristics in study arms Low risk No significant differences in socio‐demographics or smoking characteristics were noted.
Contamination of control group Low risk Very unlikely ‐ as clear voucher schemes for abstinence and non‐abstinence.