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Small for gestational age trends in Canada from 2000-2016 : an analysis of individual-level factors and the minimum wage El Adam , Shiraz


Background Earlier studies investigating birthweight trends in Canada indicated a downward trend in SGA births. Today, evidence suggests an unexplained upward trend, as well as regional differences, in SGA births from 2005-2014. These variations, over time and across jurisdictions, might be explained through downstream individual-level risk factors and/or more upstream contextual factors such as the minimum wage. Recent studies in the US found that higher minimum wages were associated with fewer adverse birth outcomes. Given the differences between the two countries, it is unclear if similar effects might be observed in Canada. Objective Describe and analyze trends in SGA births across Canada from 2000 to 2016 using individual and contextual-level data and then explore the association between minimum wage and SGA outcomes. Methods Retrospective cross-sectional analyses of all singleton births in Canada from 2000-2016 modeled SGA births through logistic regression, adjusting for individual and contextual risk factors. These models were then further adjusted for real minimum wage lagged by nine months. Analyses in both studies were stratified by four provinces (Ontario, Quebec, Alberta, and BC). Two subgroup analyses on single and all mothers residing in low income neighborhoods were further conducted. Results A secular upward trend in SGA births extended from 2000-2016 and was not completely explained by changes in maternal age, parental birthplace, marital status, community size and neighborhood income quintile. A dollar increase in real minimum wage was associated with 2% lower odds of an SGA birth (95% CI 0.97, 0.99), when adjusting for all other confounders. Provincially-stratified analyses and subgroup analysis of mothers in low income neighbourhoods, however, had null findings. For single mothers residing in low income neighbourhoods, a dollar increase in real minimum wage was associated with 3.0% [95% CI: 1.01, 1.05] higher odds of an SGA birth, adjusting for all other confounders. Conclusion SGA trends in Canada result from complex interactions of many variables. Not all of these variables, including risk factors such as smoking, were available at an individual level for analysis. Intermediate income and employment pathways between real minimum wage and SGA births, specifically for low income single mothers, require further exploration.

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