Declining maternal smoking prevalence did not change low birthweight prevalence in Massachusetts from 1989 to 2004.

BACKGROUND Maternal smoking is associated with low birthweight (LBW). LBW prevalence is increasing in the US. However, it is unclear whether a fall in maternal smoking has any impact on the LBW prevalence in Massachusetts, a state with a comprehensive tobacco control program since 1993. METHODS Temporal patterns in prenatal maternal smoking and in LBW prevalence were quantified between 1989 and 2004, using Massachusetts Community Health Information Profile database. Yearly population-attributable-risk (PAR %) of singleton LBW live-births among pregnant smoking mothers were estimated based on a summary relative risk. The expected number of LBW babies attributable to reductions in maternal smoking in 2004 relative to 1989 was compared to the actual number of LBW babies in 2004. RESULTS Of 88 929 and 74 554 singleton live-births, 4297 and 4004 LBW births occurred in 1989 and 2004, respectively. Between 1989 and 2004, maternal smoking prevalence significantly declined yearly by >or=6% (from 19.9% to 6.8%) but overall LBW prevalence increased yearly by <1% (from 4.8% to 5.4%), with a significant yearly increase (<1%) in moderately LBW (1500-2499 g) prevalence. Yearly PAR % declined from 20.3% (n = 872) to 8.0% (n = 320), with an expected total of 3745 [4297 - (872 - 320)] LBW babies in 2004 relative to 1989. However, actual LBW babies numbered 4004 in 2004. The 259 above predicted (4004 - 3745) LBW babies born in 2004 being attributed to factors other than prenatal maternal smoking. CONCLUSIONS Massachusetts experienced a decline in prenatal maternal smoking prevalence, but an increase in moderately LBW prevalence has offset the potential gains apparently achieved due to reductions in maternal smoking prevalence.