RCTs that evaluated the efficacy of smoking cessation counselling among pregnant smokers were included. Minimal clinical interventions (brief advice), individual counselling, group counselling and telephone counselling were eligible. Definitions of interventions and control were provided by the review authors. Trials had to report a biochemically validated measure of abstinence at six or 12 months follow-up. Abstinence was measured as continuous abstinence (no smoking from initial quit data until the end of follow-up) or prevalence at a specific point in time (no smoking during a given period, generally in the past seven days).
Trials that did not have usual care as a control group were excluded. Studies that evaluated self-help or educational interventions other than counselling and studies that randomised physicians, therapists or centres instead of women were excluded. Studies that included two or more types of counselling or had a cointervention that was not used in both treatment groups were excluded. Most studies were conducted in USA and two were from UK.
Most of the women were from the general population. Where reported, participants smoked on average between 12 and 28 cigarettes a day. Most participants received one-to-one and face-to-face counselling and a few received a telephone intervention. The number of counselling sessions ranged from three to nine, with a total duration of between 180 and 600 minutes.
The authors did not state how many reviewers selected the studies.