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.