Smoking behaviour in pregnancy and its impact on smoking cessation at various intervals during follow-up over 21 years: a prospective cohort study

Abstract

Objective: To determine whether mothers who quit or reduce their level of smoking in pregnancy comprise a group of health-conscious women who are disproportionally likely to adopt a healthier smoking lifestyle in the medium to longer term, compared with women who continue to smoke during pregnancy.

Design: A prospective cohort study.

Setting: A public hospital in Australia.

Population: A cohort of 6703 individual mothers who completed both initial phases of data collection in 1981-1983; mothers who smoked daily (2992) before pregnancy were included in this study.

Methods: Mothers were interviewed at 3-5 days post-delivery, 6 months, 5 years, 14 years and 21 years to determine their smoking status. An inverse probability-weighted Poisson regression with a robust error variance was fitted to the data using a log-link function and a binary response variable for smoking outcome, and adjusting for several possible confounding factors.

Main outcome measure: Smoking cessation at several follow-up points, for up to 21 years.

Results: Of the mothers who smoked daily before pregnancy, 12, 23, 37 and 41% reported having ceased smoking at 6 months and at 5, 14 and 21 years, respectively. The decision to quit smoking during pregnancy was found to be independently associated with a higher rate ratio (RR) of smoking cessation at 6 months (RR 30.60, 95% CI 20.50-45.69), 5 years (RR 4.36; 95% CI 3.61-5.27), 14 years (RR 2.42, 95% CI 2.12-2.75) and 21 years (RR 1.86; 95% CI 1.60-2.15), after adjusting for several possible confounding factors.

Conclusions: Pregnancy appears to be an opportunity for successfully quitting smoking, regardless of socio-economic circumstances or demographic background.