How did Smoking Affect Birth Outcomes in Massachusetts from 1989 to 2004?

Purpose Massachusetts introduced a comprehensive tobacco control program (MTCP) in January 1993. Tobacco smoke is a serious health hazard, particularly for pregnant women. Low birth weight (LBW) is a common condition that has been shown consistently to be causally related to smoking during pregnancy. Methods We calculated population attributable risk (PAR), using the conventional formula in addition to the effect measure, which is relative risk (RR) in this study. Because the database used (Mass CHIP) captures all pregnant women including their smoking status across the state, and also links birth files with death files, this database is a valuable resource for calculating overall smoking prevalence among pregnant women. Infant mortality rates (IMR) from 1989 to 2004 were also calculated. Multiple births and pregnant women with unknown smoking status (<1%) were excluded from the analysis. LBW was classified into three groups (0–1499 grams, 1500–2499 grams and ≥2500 grams). Results More than 91,000 live-births occurred in 1989 as opposed to 78,250 live-births in 2004. Almost 22% of mothers smoked during pregnancy in 1989, reducing to 7.4% in 2004 (66% decline). IMR among smoking mothers declined from 11.6/1000 live-births in 1989 to 5.7 in 2004 (>50% decline), while IMR in non-smoking mothers decreased from 6.7 in 1989 to 4.2/1000 live-births in 2004 (a 37% decline). The proportions of sudden infant death syndrome babies showed a significant annual decline of -6% among non-smokers. The very low LBW babies among smokers showed an annual decline of 8.4% (95%CI: -9.1; -7.7). In the 15-year study period, RR of LBW among smokers has decreased from 2.0 to 1.71 (a 29% overall decline). PAR decreased from 18% to 5% over the 15-year period contributing to almost 300 fewer LBW babies between 1989 and 2004. Conclusion Approximately 300 fewer LBW babies were born between 1989 and 2004 in Massachusetts that could be attributed to reductions in smoking prevalence during pregnancy. Such an effect can also in part be due to the beneficial impact of the MTCP. The fact that almost 5,800 pregnant mothers still continue smoking is of concern. Health promotional activities should be focused on target populations both for an accelerated decline and for a substantial impact.