Background: Environmental tobacco smoke has an adverse impact on 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 analyse short-term effects of smoke-free legislation on birth
weight, low birth weight, gestational age, preterm birth and small for gestational age.
Results: We analysed 1,800,906 pregnancies resulting in singleton live-births in England
between January 1 2005 and December 31 2009. In the one to five months following the
introduction of the smoking-free legislation, for those entering their third trimester, the risk of
low birth weight decreased by between 8% (95% 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 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 beneficial
impact on birth outcomes overall, although this benefit was not observed across all age, ethnic, or
deprivation groups.