Secular trends in smoking during pregnancy according to income and ethnic group: four population-based perinatal surveys in a Brazilian city.

OBJECTIVES: To assess socioeconomic and ethnic inequalities in smoking during pregnancy over three decades (1982-2011). SETTING: Population-based study in Pelotas City, Brazil. PARTICIPANTS: All urban women giving birth in the city hospitals in 1982 (5909), 1993 (5223) and 2004 (4201), plus all urban and rural women delivering from January 2011 to April 2012 (6275). PRIMARY OUTCOME: Self-reported smoking during pregnancy. RESULTS: The prevalence of smoking during pregnancy fell from 35.7% in 1982 to 21.0% in 2011. In each survey, prevalence decreased with increasing income (p<0.001). In the poorest quintile, smoking fell by 27.4% in the period studied compared to 67.1% in the wealthiest quintile. In all surveys, prevalence was lower among white women than among those who classified themselves as black or brown (p<0.001). Over time, smoking declined by 50.0% among the former and 30.7% among the latter. Absolute and relative inequalities both increased over time. CONCLUSIONS: The reduction in smoking during pregnancy was primarily due to a decline among white, high-income women. Further efforts are needed to reduce smoking among all population groups.