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Protective Effects of Smoke-free Legislation on Birth Outcomes in England: A Regression Discontinuity Design

Bakolis, Ioannis; Kelly, Ruth; Fecht, Daniela; Best, Nicky; Millett, Christopher; Garwood, Kevin; Elliott, Paul; Hansell, Anna L.; Hodgson, Susan

doi: 10.1097/EDE.0000000000000534
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Background: Environmental tobacco smoke has an adverse association with preterm birth and birth weight. England introduced a new law to make virtually all enclosed public places and workplaces smoke free on July 1, 2007. We investigated the effect of smoke-free legislation on birth outcomes in England using Hospital Episode Statistics (HES) maternity data.

Methods: We used regression discontinuity, a quasi-experimental study design, which can facilitate valid causal inference, to analyze short-term effects of smoke-free legislation on birth weight, low birth weight, gestational age, preterm birth, and small for gestational age.

Results: We analyzed 1,800,906 pregnancies resulting in singleton live-births in England between 1 January 2005 and 31 December 2009. In the 1 to 5 months following the introduction of the smoke-free legislation, for those entering their third trimester, the risk of low birth weight decreased by between 8% (95% confidence interval [CI]: 4%, 12%) and 14% (95% CI: 5%, 23%), very low birth weight between 28% (95% CI: 19%, 36%) and 32% (95% CI: 21%, 41%), preterm birth between 4% (95% CI: 1%, 8%) and 9% (95% CI: 2%, 16%), and small for gestational age between 5% (95% CI: 2%, 8%) and 9% (95% CI: 2%, 15%). The estimated impact of the smoke-free legislation varied by maternal age, deprivation, ethnicity, and region.

Conclusions: The introduction of smoke-free legislation in England had an immediate estimated beneficial impact on birth outcomes overall, although we did not observe improvements across all age, ethnic, or deprivation groups.

See video abstract at http://links.lww.com/EDE/B85.

Supplemental Digital Content is available in the text.

From the aUK Small Area Health Statistics Unit & MRC-PHE Centre for Environment and Health, School of Public Health, Department of Epidemiology and Biostatistics, Imperial College London, London, United Kingdom; bHealth Services and Population Research Department, Institute of Psychiatry, Psychology and Neuroscience, King’s College London, London, United Kingdom, cDepartment of Biostatistics, Institute of Psychiatry, Psychology and Neuroscience, King’s College London, London, United Kingdom; dDepartment of Epidemiology and Biostatistics, School of Public Health, Imperial College London, London, United Kingdom; eThe Medical Research Council, London, United Kingdom; fDepartment of Primary Care and Public Health, School of Public Health, Imperial College London, London, United Kingdom; gDirectorate of Public Health and Primary Care, Imperial College Healthcare NHS Trust, London, United Kingdom; and hMRC-PHE Centre for Environment and Health, Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, London, United Kingdom.

Submitted 5 June 2015; accepted 8 July 2016.

The work of the UK Small Area Health Statistics Unit is funded by Public Health England as part of the MRC-PHE Centre for Environment and Health, funded also by the UK Medical Research Council. Hospital Episode Statistics data are copyright © 2014, re-used with the permission of the Health and Social Care Information Centre. All rights reserved. CM is funded by an NIHR Research Professorship.

The authors report no conflicts of interest.

Supplemental digital content is available through direct URL citations in the HTML and PDF versions of this article (www.epidem.com).

Correspondence: Susan Hodgson, Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, London W2 1PG, United Kingdom. E-mail: susan.hodgson@imperial.ac.uk.

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