Decreasing smoking prevalence during pregnancy in Sweden: the effect on small-for-gestational-age births.

OBJECTIVES: This study examined whether recent changes in smoking prevalence among pregnant women have affected risks of small-for-gestational-age births. METHODS: With data for all live single births in Sweden from 1983 through 1992 (n = 1048139), odds ratios ORs] and attributable risks of small-for-gestational-age births were calculated for 1983 through 1985, 1986 through 1989, and 1990 through 1992. RESULTS: Daily smoking decreased from 29.4% in 1983 to 21.8% in 1992. For the three time periods, the odds ratios of small-for-gestational-age births by maternal smoking were almost identical: 1-9 cigarettes/day OR = 2.1 or 2.2; for > or = 10 cigarettes/day, OR = 2.8. The attributable risk of smoking for small-for-gestational-age births declined from 26.2% in 1983 through 1985 to 20.9% in 1990 through 1992. CONCLUSIONS: The findings point to a true decrease in tobacco exposure during pregnancy and a reduction in the attributable risk for small-for-gestational-age births.