Impact of Smoke-free Legislation on Early-life Mortality and Low Birth Weight in England: a Quasi-experimental Study

Primary research question Has there been a change in the numbers of babies being born with low birth weight or dying in the perinatal or infant period following the 1 July 2007 introduction of a ban on smoking in public places in England?

Study design Retrospective cohort study (using prospective routinely collected health care data)

Study population All singleton births in England between 1 January 1995 and 31 December 2011.

Intervention The intervention under study is the ban on smoking in enclosed public places and the workplace implemented in England overnight on 1 July 2007.

Inclusion and exclusion criteria We will include all registered singleton births in England occurring between 1 January 1995 and 31 December 2011. This is the maximum time period surrounding the ban's introduction for which the required birth data are available through the data source. Data were originally extracted for 1 January 1993 to 31 December 2011. However, postcode was not recorded in 1993-1994, leading to missing values for Index of Multiple Deprivation (IMD) quintile, region, and urbanisation level in this period. As these variables were considered key potential confounders in the primary analyses, a decision was made to restrict the modelling to the time period 1 January 1995-31 December 2011.