Abstract
BackgroundMeta-analyses of studies investigating the impact of maternal environmental tobacco smoke (ETS) on birth weight have not produced robust findings. Although, ante natal ETS exposure probably reduces infant's birth weights, the scale of this exposure remains unknown. We conducted a large, cohort study to assess the impact of ETS exposure on birth weight whilst adjusting for the many factors known to influence this.MethodRetrospective study using interview data from parents of 18,297 children born in 2000/2001 and living in the UK 9 months afterwards (the Millennium Cohort Survey). Comparison of birth weight, sex and gestational age specific (SGA) z score, birth before 37 weeks and birth weight < 2.5 Kg (LBW) in infants born to women exposed to: i) no tobacco smoke, ii) ETS only and iii) maternal smoking whilst pregnant.Results13% of UK infants were exposed to ETS and 36% to maternal smoking ante natally. Compared to no ante natal tobacco smoke exposure, domestic ETS lowered infants' adjusted mean birth weights by 36 g (95% CI, 5 g to 67 g) and this effect showed a dose-response relationship. ETS exposure also caused non-significant increases in the adjusted risks of Low Birth Weight (<2.5 Kg) [OR 1.23 (95% CI, 0.96 to 1.58) and premature birth [OR 1.21 (95% CI, 0.96 to 1.51)], whilst the impacts of maternal smoking were greater and statistically significant.ConclusionUK prevalences of domestic ETS exposure and maternal smoking in pregnancy remain high and ETS exposure lowers infants' birth weights.
Highlights
Meta-analyses of studies investigating the impact of maternal environmental tobacco smoke (ETS) on birth weight have not produced robust findings
ETS exposure had no impact on the risk of either small for gestational age (SGA) or low birth weight (LBW) at term alone and the reviewers noted that empirical studies were conducted in widely varied settings and often small and of poor quality, reporting only crude birth outcomes
We report the findings of such a study using data from the Millennium Survey, a contemporary UK epidemiological birth cohort, to investigate the UK prevalences of domestic ETS exposure and maternal smoking in pregnancy and the relative impact of these exposures on birth weight
Summary
Meta-analyses of studies investigating the impact of maternal environmental tobacco smoke (ETS) on birth weight have not produced robust findings. Studies investigating whether or not maternal ETS exposure during pregnancy affects birth outcomes have reported mixed findings [9,10]. A review [9] found significant heterogeneity between studies, but still presented synthesised findings and concluded that maternal ETS exposure during pregnancy reduced infants' adjusted mean birth weights by -24.0 g [95% CI -39.3 g to -8.6 g] and increased the risks of babies being either "small for gestational age (SGA) or LBW at term" [9]. Previously calls for large, well-conducted cohort studies which have sufficient power to assess the impact of ETS exposure on birth outcomes whilst adjusting for the many factors known to influence these [9] remain relevant today[12]. We report the findings of such a study using data from the Millennium Survey, a contemporary UK epidemiological birth cohort, to investigate the UK prevalences of domestic ETS exposure and maternal smoking in pregnancy and the relative impact of these exposures on birth weight
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