Fig. 1

Study sampling frame and sample. Two thousand four hundred and seventy-four women between January and December 2012 replied ‘Yes’ when asked by their midwife at their maternity booking visit if they had smoked at least one cigarette in the last week. Seven hundred and fifty-two had a carbon monoxide level (CO) less than 7 ppm, or unavailable in 172 (7 %); 13 (<1 %) were under 16 years of age; 243 (10 %) had a gestation ≥24 weeks; 593 (24 %) were not contactable by the Stop Smoking Service (SSS); 23 (<1 %) were non-English speaking; the trial was not discussed by the SSS with 31 (1 %); and permission was not obtained to pass contact details for 113 (5 %). These categories are not mutually exclusive. The remaining 823 (33 % of all self-reported smokers) were eligible for the trial and were passed to the trial team. A records check showed that five had miscarried and contact was not attempted. Three hundred and one could not be contacted by the trial team. Of the 517 contacted, 6 had miscarried and 16 did not consent to the trial. Of the 495 who consented and were randomised, 3 control participants opted out and did not want any data collected in the trial to be used leaving 492 trial participants with data for analysis making up group A. All self-reported smokers who were not included in the trial analysis (2474–492) made up group B (n = 1982)