Smoking rates have dropped substantially in most developed countries in recent decades. This general trend has, however, not always been evident among women-particularly younger women. Smoking habits do, however, often change in connection with pregnancy and the aim of this study is to determine whether smoking during pregnancy follows general trends in smoking rates in the general female population in four countries with active anti-tobacco policies and decreasing population smoking rates.Changes in rates of persistent smoking, that is, smoking in late pregnancy or daily smoking among all women of childbearing age were described according to age groups. Data were retrieved from the Australian Household Drug Surveys during 2000-2013 and from registries and surveys in Finland, Norway, and Sweden between 1995 and 2014.In general, persistent smoking has decreased and late-pregnancy smoking rates are lower than daily smoking rates among all women. However, younger women are more likely to be persistent smokers regardless of pregnancy status. In Norway and Finland, persistent smoking was most common among young pregnant women and in Sweden there was an increased polarization between age groups. In Australia, a steady decrease in smoking rates appears to have stalled in younger pregnant women.Although smoking has declined substantially in recent decades, there are groups lagging behind this general trend. Young pregnant women are of particular concern in this respect. The possibility that these findings reflect the changing characteristics of younger pregnant women is discussed.This study puts recent trends in maternal smoking into a broader context by relating developments to changes in smoking rates among women in general. By using similar data from four countries we were able to follow changes in smoking rates "within" groups of women within the four countries without being limited by methodological problems related to cross-country or inter-group comparisons. We were above all able to show that aggregate data disclose the strong age gradient in maternal smoking habits.