Partner's smoking: a major determinant for changes in women's smoking behaviour during and after pregnancy.

To study determinants for changes in maternal smoking behaviour during and after pregnancy, questionnaire information on smoking habits was recorded in a cohort of 3710 Norwegian women during early pregnancy, at delivery, and one year later. Of 3039 cohabiting women with complete information on smoking at all three occasions 31% smoked in early pregnancy 23% in the late pregnancy and 28% one year after delivery. Among the cohabiting mothers who smoked in early pregnancy, 44% stopped during pregnancy. After adjusting for confounding factors, the odds ratio for smoking cessation among these women who had cohabitants who smoked as opposed to not smoking was 0.2 (95% CI: 0.1-0.2). Among cohabiting non-smoking women during late pregnancy the odds ratio for being a smoker one year after child birth was 3.0 (95% CI: 2.2-4.0), if their cohabitants smoked as opposed to not smoking. The women's smoking behaviour changes considerably during and after pregnancy and their cohabitants' smoking seems to be a major determinant for changes in their smoking behaviour.