• Deborah Shipton, David M Tappin, Thenmalar Vadiveloo, Jennifer A Crossley, David A Aitken, and Jim Chalmers.
• MRC Social and Public Health Sciences Unit, Glasgow G12 8RZ.
• BMJ. 2009 Jan 1; 339: b4347.

ObjectiveTo determine what impact reliance on self reported smoking status during pregnancy has on both the accuracy of smoking prevalence figures and access to smoking cessation services for pregnant women in Scotland.DesignRetrospective, cross sectional study of cotinine measurements in stored blood samples.ParticipantsRandom sample (n=3475) of the 21 029 pregnant women in the West of Scotland who opted for second trimester prenatal screening over a one year period.Main Outcome MeasureSmoking status validated with cotinine measurement by maternal area deprivation category (Scottish Index of Multiple Deprivation).ResultsReliance on self reported smoking status underestimated true smoking by 25% (1046/3475 (30%) from cotinine measurement v 839/3475 (24%) from self reporting, z score 8.27, P<0.001). Projected figures suggest that in Scotland more than 2400 pregnant smokers go undetected each year. A greater proportion of smokers in the least deprived areas (deprivation categories 1+2) did not report their smoking (39%) compared with women in the most deprived areas (22% in deprivation categories 4+5), but, because smoking was far more common in the most deprived areas (706 (40%) in deprived areas compared with 142 (14%) in affluent areas), projected figures for Scotland suggest that twice as many women in the most deprived areas are undetected (n=1196) than in the least deprived areas (n=642).ConclusionReliance on self reporting to identify pregnant smokers significantly underestimates the number of pregnant smokers in Scotland and results in a failure to detect over 2400 smokers each year who are therefore not offered smoking cessation services.

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