Change in smoking status during two consecutive pregnancies : a population-based cohort study

Objective. To investigate changes in tobacco smoking in two consecutive pregnancies and factors associated with the change. Design Population-based cohort study. Setting. New South Wales, Australia, 2000-10. Population. A total of 183 385 women having first and second singleton pregnancies. Methods. Descriptive and multivariable logistic regression analyses of perinatal data linked to hospital admission data. Main outcome measures. Proportion of women smoking during their first pregnancy who quit by their second, and of women not smoking in their first pregnancy who did smoke during their second. Results. Among 22 761 smokers in the first pregnancy, 33.5% had quit by their second. Among 160 624 non-smokers in their first pregnancy, 3.6% smoked during their second. Women who were aged ≥25 years, were married, born in a non-English speaking country, used private obstetric care, and lived in a socio-economically advantaged area were more likely to quit or less likely to start smoking in the second pregnancy. Smokers who had gestational hypertension (adjusted odds ratio [OR] 1.36, 95% confidence interval [95% CI] 1.23-1.51), a large-for-gestational age infant (OR 1.66, 95% CI, 1.46-1.89), and a stillbirth (OR 1.44, 95% CI 1.06-1.94) were more likely to quit, whereas smokers whose infant was small-for-gestational-age (OR 0.65, 95% CI 0.60-0.70) or admitted to special care nursery (OR 0.87, 95% CI 0.81-0.94) were less likely to quit. Among non-smokers in the first pregnancy, the risk of smoking in the second pregnancy increased with late antenatal attendance (e.g. ≥26 weeks, OR 1.30, 95% CI 1.14-1.48), gestational diabetes (OR 1.25, 95% CI 1.07- 1.45), preterm birth (e.g. spontaneous, OR 1.25, 95% CI 1.10- 1.43), caesarean section (e.g. prelabour, OR 1.13, 95% CI 1.01- 1.26), and infant small-for-gestational-age (OR 1.37, 95% CI 1.26- 1.48) or required special care nursery (OR 1.14, 95% CI 1.06- 1.23). Inter-pregnancy interval of ≥3 years was associated with either change in smoking status. Conclusions, Most smokers continue to smoke in their next pregnancy, even among those who experienced poor outcomes. Intensive interventions should be explored and offered to women at the highest risk.