A citywide smoking ban reduced maternal smoking and risk for preterm births: a Colorado natural experiment

Few reports exist on the association of a public smoking ban with fetal outcomes and maternal smoking in the United States. We sought to evaluate the effect of a citywide smoking ban in comparison to a like municipality with no such ban in Colorado on maternal smoking and subsequent fetal birth outcomes.

A citywide smoking ban in Colorado provided a natural experiment. The experimental citywide smoking ban site was implemented in Pueblo, Colorado. A comparison community was chosen that had no smoking ban, El Paso County, with similar characteristics of population, size, and geography. The two sites served as their own controls, as each had a preban and postban retrospective observation period: preban was April 1, 2001, to July 1, 2003; postban was April 1, 2004, to July 1, 2006. Outcomes were maternal smoking (self-report), low birth weight (LBW) (defined as <2500 g or as <3000 g), and preterm births (<37 weeks gestation) in singleton births from mothers residing in these cities and reported to the State Department of Public Health. A difference-in-differences estimator was used to account for site and temporal trends in multivariate models.

Compared to El Paso County preban, the odds of maternal smoking and preterm births were, respectively, 38% (p<0.05) and 23% (p<0.05) lower in Pueblo. The odds for LBW births decreased by 8% for <3000 g and increased by 8.4% for <2500 g; however, neither was significant.

This is the first evidence in the United States that population-level intervention using a smoking ban improved maternal and fetal outcomes, measured as maternal smoking and preterm births.