Air pollution, neighbourhood and maternal-level factors modify the effect of smoking on birth weight: a multilevel analysis in British Columbia, Canada

Abstract

BackgroundMaternal smoking during pregnancy negatively impacts fetal growth, but the effect is not homogenous across the population. We sought to determine how the relationship between cigarette use and fetal growth is modified by the social and physical environment.MethodsBirth records with covariates were obtained from the BC Perinatal Database Registry (N = 232,291). Maternal smoking status was self-reported as the number of cigarettes smoked per day usually at the first prenatal care visit. Census dissemination areas (DAs) were used as neighbourhood-level units and linked to individual births using residential postal codes to assign exposure to particulate air pollution (PM2.5) and neighbourhood-level attributes such as socioeconomic status (SES), proportion of post-secondary education, immigrant density and living in a rural place. Random coefficient models were used with cigarettes/day modeled with a random slope to estimate its between-DA variability and test cross-level interactions with the neighbourhood-level variables on continuous birth weight.ResultsA significant negative and non-linear association was found between maternal smoking and birth weight. There was significant between-DA intercept variability in birth weight as well as between-DA slope variability of maternal smoking on birth weight of which 68 and 30 % respectively was explained with the inclusion of DA-level variables and their cross-level interactions. High DA-level SES had a strong positive association with birth weight but the effect was moderated with increased cigarettes/day. Conversely, heavy smokers showed the largest increases in birth weight with rising neighbourhood education levels. Increased levels of PM2.5 and immigrant density were negatively associated with birth weight, but showed positive interactions with increased levels of smoking. Older maternal age and suspected drug or alcohol use both had negative interactions with increased levels of maternal smoking.ConclusionMaternal smoking had a negative and non-linear dose-response association with birth weight which was highly variable between neighbourhoods and evidence of effect modification with neighbourhood-level factors. These results suggest that focusing exclusively on individual behaviours may have limited success in improving outcomes without addressing the contextual influences at the neighbourhood-level. Further studies are needed to corroborate our findings and to understand how neighbourhood-level attributes interact with smoking to affect birth outcomes.

Cumulative exposure to environmental pollutants during early pregnancy and reduced fetal growth: the Project Viva cohort

“…The prior literature on the association between traffic pollution and birth outcomes for woman prenatally exposed versus not exposed to cigarette smoke is conflicting and limited. Specifically, in a study of over 200,000 Canadian births, maternal smoking attenuated the association between air pollution exposure and low birth weight [ 42 ], whereas a study of over 600,000 U.S. births found the association between high prenatal traffic-related carbon monoxide exposure and low birth weight to be larger among smoking versus non-smoking mothers [ 43 ]. In a U.S. urban cohort of over 200 non-smoking pregnant women, passive smoke exposure and a blood marker of ambient air pollution (benzo[a]pyrene-DNA adducts) synergistically lowered birth weight, although there were not independent associations between either exposure with birth weight [ 44 ].…”

Birth outcome racial disparities: A result of intersecting social and environmental factors

“…Associations may be partially attributable to personal habits such as smoking, which is more common among women with lower education levels, but models including both smoking and education reveal independent associations of each of these factors with birth outcomes such as birth weight. 15 This suggests that low educational attainment may work through other pathways to lead to adverse birth outcomes. Additionally, equity in education is unlikely to eliminate disparities in birth outcomes.…”

Gehiegizko pisua 0-7 urteko adineko umeengan. Arrisku-faktoreak

“…Faktore horrek maila sozioekonomikoarekin lotura dauka, maila baxuagoko familiek gehiago erretzen dutelako (13). Maila sozioekonomiko altuak eragin positiboa zuen jaiotzako pisuan ikerketa batean (20), baina amek erretzen zutenean efektu onuragarri hori galdu egiten zen.…”