Methods	Quasi-randomised (allocation by birth date) trial of smoking cessation intervention based on RA Windsor self-help manual in 13/14 public health maternity clinics in Gothenburg, Sweden 1987-1988
Participants	Women who spoke Swedish, smoking >= 1 cigarette/day, gestational age <12 weeks at first antenatal visit, (no other exclusion criteria specified), leaving n = 745 of whom 22 had quit by the second antenatal visit. 15% refused to take part (−75) leaving 417 in the intervention and 231 in the control group
Interventions	All women were advised to quit by the midwife at the first antenatal clinic; pre-intervention. Control: basic information sheet given to women by the doctor with basic facts about smoking and pregnancy and recommendation to quit. Intervention: self-help manual based on Windsor 1985, revised and with new parts added, distributed by the obstetrician at the second antenatal visit. Self-help tasks were based on principles of behavioural therapy. Intensity rating: I = 3, C = 2
Outcomes	Smoking cessation data; biochemically validated (blood thiocyanate <100 ng/ml) at first and second antenatal visit and in late pregnancy, and 8 weeks’ postpartum; mean birthweight; low birthweight; preterm birth (< 36 weeks) Smoking reduction in mean cigarettes per day (the standard deviation for the mean was not provided so in the analysis it was calculated from the confidence intervals given in the paper)
Notes	Same data published by Svanberg 1992. No process evaluation.
Risk of bias
Item	Authors’ judgement	Description
Adequate sequence generation?	No	By birthday. Uneven groups.
Allocation concealment?	No	Possible to predict allocation.
Blinding? Women and clinical staff	No	Neither provider nor women blinded to this educational intervention
Incomplete outcome data addressed? All outcomes	No	Attrition in both groups, approximately 15% in the experimental group at the outset and 11% later. No ITT analysis. Some loss to follow up but where data were available all cases were included
Free of selective reporting?	Unclear	Not apparent.
Free of detection bias?	Yes	Serum thiocyanate analysis at 30-34 weeks’ gestation and postpartum