Donatelle 2000a.

Methods	Study design: RCT, conducted June 1996 to June 1997; data collection completed January 1998 Country: USA Setting: 4 Oregon Women, Infants, and Children (WIC) programme sites SOS (Significant Other Supporter) Programme I
Participants	220 women smokers (112 intervention, 108 control) Aged 15+, ≤ 28 weeks gestation, literate in English; withdrawal criteria included termination and foetal death
Interventions	All participants received a USD 5 participation voucher at each of 3 assessments. Everyone at baseline was given verbal and written advice on importance of smoking cessation by WIC‐ or SOS‐trained staff, + self‐help kit A pregnant woman’s guide to quit smoking Experimental Group(s): Each participant was asked to designate a social supporter, preferable female non‐smoker. Both were eligible for vouchers if participant quit. Participant was phoned monthly (up to 10 months) to report smoking status. If she reported quit and supplied confirmatory saliva sample, she got a USD 50 voucher, and “their social supporter received a voucher as well” (i.e. USD 50 for 1st quit month, USD 25 for other quit months, and USD 50 for final quit month). Vouchers were funded by contributions from 10 local 'community partners' (businesses, foundations and healthcare organisations) Control Group: Baseline advice and quit kit, + monthly phone calls to determine smoking status
Outcomes	7‐day PPA at 8 months gestation, and at 2 months post‐partum Biochemical validation by salivary cotinine < 30 ng/ml, and salivary thiocyanate < 100 mg/ml
Notes	New for 2015 update Funding: grant from Robert Wood Johnson Foundation Smoke‐Free Families Program, + support from local businesses and healthcare facilities
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not stated
Allocation concealment (selection bias)	Unclear risk	Not stated
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Abstinence biochemically validated
Incomplete outcome data (attrition bias) All outcomes	High risk	Relatively high, but comparable with non‐participant attenders at the WIC clinic Losses: Intervention: 32% at 8 months gestation, 36% at 2 months post‐partum; Control: 51.5% at 8 months gestation, 52% at 2 months post‐partum