The impact of changing smoking habits and smoke-free legislation on orofacial cleft incidence in the United Kingdom: evidence from two time-series studies

Abstract

Objectives: To 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. Design: First, 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. Setting: United Kingdom. Population: All children born between 2000 and 2018 and their mothers. Main outcome measures: Orofacial cleft incidence, reported annually for England, Wales and Northern Ireland and separately for Scotland. Results: Over 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. Conclusion: These 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.