Objective This study describes trends (1994–2007) in smoking in pregnancy (SIP) among an Australian population sample of women. This study also examines trends in the socioeconomic distribution of SIP over the 14-year period.

Methods Bivariate and multiple logistic regression analyses of the NSW Midwives Data Collection were used to explore the associations and trends in SIP by sociodemographic factors.

Results The prevalence of SIP in New South Wales (NSW) declined from 22.1% (1994) to 13.5% in 2007. However, the largest decrease in SIP rates was among the highest socioeconomic group (67.9% decline), and smaller declines were observed among teenage and remote rural mothers. Maternal age, ethnicity, Aboriginality, area of remoteness and socioeconomic status were independently associated with SIP. The distribution of NSW mothers has changed, with fewer younger mothers and more from an Asian background.

Conclusion This study reported large declines in SIP prevalence, with a population effect similar to that expected following exposure to (Cochrane-defined) intensive behavioural interventions. However, no specially targeted public health efforts were made during this period to influence SIP, so that social norm change is the likely explanation for these population health changes. The relative decline in SIP was smaller among low-socioeconomic status mothers, by language spoken at home, Aboriginality and area of remoteness, suggesting that inequalities in SIP have increased over this 14-year period. This information informs equity-based approaches to targeting further smoking cessation programs for pregnant Australian women.