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Impact of a stepwise introduction of smoke-free legislation on the rate of preterm births: analysis of routinely collected birth data

BMJ 2013; 346 doi: (Published 14 February 2013) Cite this as: BMJ 2013;346:f441
  1. Bianca Cox, PhD student1,
  2. Evelyne Martens, MSc student2,
  3. Benoit Nemery, professor3,
  4. Jaco Vangronsveld, professor1,
  5. Tim S Nawrot, associate professor of environmental epidemiology13
  1. 1Centre for Environmental Sciences, Hasselt University, Agoralaan gebouw D, 3590 Diepenbeek, Belgium
  2. 2Study Centre for Perinatal Epidemiology, Brussels, Belgium
  3. 3Department of Public Health, University of Leuven (KU Leuven), Leuven, Belgium
  1. Correspondence to: T S Nawrot tim.nawrot{at}
  • Accepted 16 November 2012


Objective To investigate the incidence of preterm delivery in the Belgian population after implementation of smoke-free legislation in three phases (in public places and most workplaces January 2006, in restaurants January 2007, and in bars serving food January 2010).

Design Logistic regression analyses on routinely collected birth data from January 2002 to December 2011.

Setting Flanders, Belgium.

Population All live born singleton births delivered at 24–44 weeks of gestation (n=606 877, with n=448 520 spontaneous deliveries).

Main outcome measures Preterm birth (gestational age <37 weeks).

Results We found reductions in the risk of preterm birth after the introduction of each phase of the smoking ban. No decreasing trend was evident in the years or months before the bans. We observed a step change in the risk of spontaneous preterm delivery of −3.13% (95% CI −4.37% to −1.87%; P<0.01) on 1 January 2007 (ban on smoking in restaurants), and an annual slope change of −2.65% (−5.11% to −0.13%; P=0.04) after 1 January 2010 (ban on smoking in bars serving food). The analysis for all births gave similar results: a step change of −3.18% (−5.38% to −0.94%; P<0.01) on 1 January 2007, and an annual slope change of −3.50% (−6.35% to −0.57%; P=0.02) after 1 January 2010. These changes could not be explained by personal factors (infant sex, maternal age, parity, socioeconomic status, national origin, level of urbanisation); time related factors (underlying trends, month of the year, day of the week); or population related factors (public holidays, influenza epidemics, and short term changes in apparent temperature and particulate air pollution).

Conclusion Our study shows a consistent pattern of reduction in the risk of preterm delivery with successive population interventions to restrict smoking. This finding is not definitive but it supports the notion that smoking bans have public health benefits from early life.


  • We thank Professor Gyselaers (department of obstetrics, East-Limburg Hospital, Genk, and faculty of life sciences and medicine, Hasselt University) for his useful comments. We thank Dr M Callens, research director of CM social security organisation, for providing figures on atosiban and cervical cerclage.

  • Contributions: TSN and BC designed the study. BC did the statistical analysis and wrote, together with TSN, the first draft of the paper. EM collected the data. All authors contributed to the discussion and interpretation of the data and the writing of the article, and approved the final version of the manuscript.

  • Funding: The Study Centre for Perinatal Epidemiology is financed and commissioned by the Flemish Centre for Care and Health (Agentschap Zorg en Gezondheid). This study was supported by grants from the Flemish Scientific fund (FWO: G.0.873.11.N.10/, ERC starting grant (ENVIRONAGE), and Hasselt University Fund (BOF).

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at (available on request from the corresponding author) and declare: no financial relationships with any organisations that might have an interest in the submitted work in the previous three years and no other relationships or activities that could appear to have influenced the submitted work

  • Ethical approval: The ethical committee of Hasselt University approved the study.

  • Data sharing: No additional data available.

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