In North America, income polarization is said to be increasing, characterized by a contracting middle-income bracket and an expansion of low- and high-income groups.1 Pregnancy can be seen as a socioeconomic stress test: having a child typically leads to increased expenses2, 3 and potential income loss, especially in the first 2 years after a birth,3, 4 which might influence residential affordability. It is not known whether there have been temporal changes in maternal neighborhood income patterns between births—especially among women residing in middle-income areas—leading to the current study. This population-based cohort study used linked administrative databases in Ontario, Canada, which has a universal healthcare system (Table S1). Included were all women with two consecutive singleton births from April 2002–March 2023 (Table S2). Use of de-identified data was authorized under section 45 of Ontario's Personal Health Information Protection Act and exempt from research ethics board (REB) review and informed consent. Study methods, variables, and analytical models are detailed in the methods supplement. Neighborhood income quintile (Q) patterns for a given woman were assessed between two consecutive births. In Cohort 1, comprising all women, income mobility was classified as downward, upward, or no change. Cohort 2 was restricted to women without residential income mobility between births, then categorized as persistently residing in either a lowest-income (Q1) neighborhood, a highest-income (Q5) neighborhood, or a middle-income (Q2, Q3, or Q4) neighborhood.5 Cohort 3 comprised all women solely residing in a middle-income neighborhood at the first birth, who were then assessed for either downward, upward or no income mobility by the second birth. Proportions and 95% confidence interval (CI) were calculated for neighborhood income Q patterns by the calendar year of the second birth. For all cohorts, annual trends were assessed using Cochran–Armitage tests. For Cohort 3, the difference in the proportion of upward minus downward income mobility at each given year was modeled using weighted linear regression analysis. There were 767 854 women included with two births (Figure S1, Table S3). In Cohort 1 (N = 767 854), approximately 55% of women, experienced no neighborhood income mobility between births, with a significant uptrend over time. Approximately 25% had upward mobility and 20% downward mobility, both of which significantly declined in annual prevalence over time (Figure 1a). In Cohort 2 (N = 425 900), comprising women with no neighborhood income mobility between births, the proportion who persisted in a middle-income area was 50% in 2004, rising significantly to 62% by 2023 (Figure 1b). In Cohort 3 (N = 479 668), among mothers exclusively residing in a middle-income neighborhood at their first birth, a greater proportion moved to a higher-income neighborhood by their second birth (Figure 1c, green line) than to a lower neighborhood (black line). There was a corresponding increase over time in the gap between moving to a higher than lower income neighborhood, from −2.6% in 2004 to +6.1% in 2023, an annual net change of +0.3% (95% CI +0.2 to +0.4) (Figure 1c, red dashed line). While pregnancy might pose a socioeconomic stress,2, 3 women residing in middle-income neighborhoods appeared more likely over time to achieve upward than downward neighborhood income mobility between births, without the initially hypothesized contraction in middle-income neighborhood dwelling. This study lacked details about a woman's individual-level income, her education, and her marital status. Neighborhood-level income measures might not be congruent with individual-level income measures. Study eligibility required two successive births per woman, which might have introduced some selection bias. Canadian women residing in middle-income areas, and who have a subsequent birth, achieved greater upward than downward neighborhood income mobility over time. Future research should assess maternal socioeconomic trajectories, contrasting women with one birth to those with multiple births, especially among the proportionately large array of women residing in middle-income areas. Further research is needed to elucidate why most women in the overall cohort did not experience neighborhood income mobility between births. JAJ had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Concept and design: JAJ and JGR. Acquisition, analysis, or interpretation of data: All authors. Drafting of the manuscript: JAJ and JGR. Critical revision of the manuscript for important intellectual content: All authors. Statistical analysis: JAJ, JG, JGR. Obtained funding: JAJ and JGR. Administrative, technical, or material support: JGR. Supervision: JGR. This study received funding from a grant from the Ontario Academic Health Sciences Centre AFP Innovation Fund and the PSI Foundation. Dr. Jairam received funding through a Keenan Postdoctoral Fellow Scholarship from the St. Michael's Hospital Foundation and a Studentship Award from the Edwin S.H. Leong Centre for Healthy Children at the University of Toronto and The Hospital for Sick Children. This study was also supported by ICES, which is funded by an annual grant from the Ontario Ministry of Health and the Ministry of Long-Term Care. The funding organizations had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication. None. The use of deidentified data in this project was authorized under section 45 of Ontario's Personal Health Information Protection Act and exempt from a research ethics board review. This document used data adapted from the Statistics Canada Postal CodeOM Conversion File, which is based on data licensed from Canada Post Corporation, and/or data adapted from the Ontario Ministry of Health Postal Code Conversion File, which contains data copied under license from ©Canada Post Corporation and Statistics Canada. This does not constitute an endorsement by Statistics Canada of this product. Parts of this material are based on data and/or information compiled and provided by the Canadian Institute for Health Information and the Ontario Ministry of Health. Parts or whole of this material are based on data and/or information compiled and provided by Immigration, Refugees and Citizenship Canada Permanent Resident (IRCC-PR) data set current to September 30, 2020. However, the analyses, conclusions, opinions, and statements expressed in the material are those of the authors, and not necessarily those of IRCC. The analyses, conclusions, opinions, and statements expressed herein are solely those of the authors and do not reflect those of the funding or data sources; no endorsement is intended or should be inferred. The dataset from this study is held securely in coded form at ICES. While legal data-sharing agreements between ICES and data providers (e.g., healthcare organizations and government) prohibit ICES from making the dataset publicly available, access might be granted to those who meet pre-specified criteria for confidential access, available at www.ices.on.ca/DAS (email: email protected). The full dataset creation plan and underlying analytic code are available from the authors upon request, understanding that the computer programs may rely upon coding templates or macros that are unique to ICES and are, therefore, either inaccessible or may require modification. Figure S1. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Jairam et al. (Fri,) studied this question.
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