The impact of changing smoking habits and smoke-free legislation on orofacial cleft incidence in the United Kingdom: evidence from two time-series studies
Authors: Fell Matthew , Russell Craig , Medina Jibby , Gillgrass Toby , Chummun Shaheel , Cobb Alistair R.M. , Sandy Jonathan , Wren Yvonne , Wills Andrew , Lewis Sarah J. 
Published: June 2021

ABSTRACTObjectivesTo analyse the association between active and passive cigarette smoking and the incidence of children born with a cleft lip and/or palate within the United Kingdom.DesignFirst, a longitudinal time-series study was conducted with routinely collected smoking prevalence data for females over 16 years of age. Second, an interrupted time-series design was used as a natural experiment to assess the impact of smoke-free legislation using segmented Poisson regression.SettingUnited Kingdom.PopulationAll children born between 2000 and 2018 and their mothers.Main outcome measuresOrofacial cleft incidence, reported annually for England, Wales and Northern Ireland and separately for Scotland.ResultsOver the study period, the annual incidence of orofacial cleft per 10,000 live births ranged from 14.2-16.2 in England, Wales and Northern Ireland and 13.4-18.8 in Scotland. The proportion of active smokers amongst females in the United Kingdom declined by 37% during the study period. Adjusted regression analysis did not show a correlation between the proportion of active smokers and orofacial cleft incidence in either dataset, although we were unable to exclude a modest effect of the magnitude seen in individual-level observational studies. The data in England, Wales and Northern Ireland suggested an 8% reduction in orofacial cleft incidence (95%CI 1% to 14%; P=0.026) following the implementation of smoke-free legislation. In Scotland, there was weak evidence for an increase in orofacial cleft incidence following smoke-free legislation.ConclusionThese two ecological studies offer a novel insight into the influence of smoking in orofacial cleft aetiology, adding to the evidence base from individual-level studies. Our results suggest that smoke-free legislation may have reduced orofacial cleft incidence in England, Wales and Northern Ireland.SUMMARY BOXSection 1: What is already known on this topicAn association between maternal active and passive smoking and orofacial cleft has been previously reported in conventional individual-level observational studiesEcological and natural experiment time-series designs have been successfully used to demonstrate the association between population-level exposures and other non-cleft health outcomesSection 2: What this study addsEcological studies within a single country with complete cleft registration data are unlikely to be sufficiently powered to detect a relationship between time-series population level trends in active smoking and the number of children born with orofacial cleft each year.In England, Wales and Northern Ireland our natural experiment study showed a reduction in the proportion of children born with an orofacial cleft following the implementation of smoke-free legislation, but this was not replicated in Scotland.This study exploits the systematic collection of population data in the UK and adds to our understanding of the role of smoking in orofacial clefting as well as demonstrating the impact of public health interventions.