Prevalence of smoking in early pregnancy by census area: measured by anonymous cotinine testing of residual antenatal blood samples

Abstract

Aim: To accurately measure the prevalence of smoking in early pregnancy by census area units (CAU) in Christchurch.

Methods: Smoking status in pregnancy was determined by serum cotinine assay for all antenatal blood samples taken over a 6 month period. CAUs in Christchurch were grouped into quartiles according to the proportion of maternal smokers. Social factors from 1991 census data were used to describe the characteristics of each quartile.

Results: The overall rate of smoking in pregnancy was 33.0%. Rates ranged from 10.6% to 56.9% for the census area groups. CAUs in the upper quartile (39-57% of women smoking in pregnancy) were clustered together geographically and were associated with lower socioeconomic indices. The strongest correlation was between average income with smoking rates (Pearson correlation coefficient 0.76).

Conclusion: Smoking rates in pregnancy have remained at around 30% for at least 20 years, with some areas of the city having rates nearly double this. It would seem logical to promote smoke-free pregnancy activities in localities with the highest rates of smoking. Future evaluation of the efficacy of such programmes should be done using objective measurements.