Benefits of smoking bans on preterm and early-term births: a natural experimental design in Switzerland

Tob Control. 2016 Dec;25(e2):e135-e141. doi: 10.1136/tobaccocontrol-2015-052739. Epub 2016 Apr 26.


Background: Birth outcomes are relevant for future children's heath. Capitalising on a natural experimental design in Switzerland, we evaluated how regional smoking bans introduced at different time points affected birth outcomes, including preterm and early-term births.

Methodology: We used birth registry data of all singleton neonates born in Switzerland (2007-2012). We developed canton-specific interrupted time-series followed by random meta-analysis to evaluate the benefits of smoking bans on preterm (<37 gestational weeks) and early-term (37-38 gestational weeks) births. Heterogeneity across type of ban and contextual characteristics was explored through metaregression. A time-to-event approach was used for evaluating duration of pregnancy under the smoking bans and effects, taking into account individual maternal factors.

Results: We observed a decrease in the risk of preterm birth of 3.6% (95% CI, -9.3% to 2.5%), and early-term birth of 5.0% (95% CI -7.5% to -2.5%). Results showed a clear dose-response relationship. Greater risk reductions were obtained for preterm births in areas with more comprehensive bans (-6.8%; 95% CI -12.1% to 0.1%), and for pregnancies with the longest gestational time under smoking bans (HR, 0.991; 95% CI 0.984 to 0.997 per 10% increase in duration). Benefits were unequal across outcomes and characteristics of cantons and mothers.

Conclusion: Smoking bans resulted in improved birth outcomes in Switzerland with cantons that adopted more comprehensive smoking bans achieving greater benefits. Early-term births constitute a previously ignored though important group.

Keywords: Prevention; Public policy; Secondhand smoke.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Female
  • Gestational Age
  • Humans
  • Infant, Newborn
  • Infant, Premature
  • Male
  • Pregnancy
  • Pregnancy Outcome / epidemiology
  • Premature Birth / epidemiology*
  • Premature Birth / etiology
  • Registries
  • Smoke-Free Policy*
  • Smoking / adverse effects
  • Smoking / legislation & jurisprudence
  • Switzerland / epidemiology
  • Tobacco Smoke Pollution / adverse effects
  • Tobacco Smoke Pollution / legislation & jurisprudence
  • Tobacco Smoke Pollution / prevention & control


  • Tobacco Smoke Pollution