Reliability of self reported smoking status by pregnant women for estimating smoking prevalence: a retrospective, cross sectional study.

Objective To 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.

Design Retrospective, cross sectional study of cotinine measurements in stored blood samples.

Participants Random 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 measure Smoking status validated with cotinine measurement by maternal area deprivation category (Scottish Index of Multiple Deprivation).

Results Reliance 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
Conclusion Reliance 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.