Disparities in Environmental Chemical Concentrations and Adverse Pregnancy Outcomes by Race and Ethnicity and Country of Birth: Examples from the MIREC Study

PURPOSE: Research investigating disproportionate exposure or susceptibility in racialized and immigrant pregnant people is limited. To address this gap, we quantified disparities in environmental chemical concentrations and pregnancy complications by two indicators: (1) race and ethnicity and (2) country of birth. Our objectives were to (1) quantify descriptive differences in chemical concentrations and prevalence of outcomes and (2) assess heterogeneity in the chemical-outcome associations by our two indicators of disparity. METHODS: Using data from a pan-Canadian longitudinal pregnancy cohort study (2008-2011), we assessed disparities in three case studies based on prior publications that examined associations between: (1) arsenic and gestational diabetes mellitus (GDM) (n = 1255), (2) lead and preterm birth (PTB) (n = 1847), and (3) perfluorohexane sulfonate (PFHxS) and hypertensive disorders of pregnancy (HDP) (n = 1739). Chemicals were measured in first trimester blood samples; lead was also measured in third trimester samples. Pregnancy complication data were extracted from medical charts. We calculated geometric mean (GM) chemical concentrations by each disparity indicator and assessed differences via one-way Analysis of Variance (ANOVA). We calculated the prevalence of each health outcome by disparity indicator and assessed differences using Chi-square tests. Using multivariable models, we assessed heterogeneity by stratifying results and calculating measures of interaction on the additive (Relative excess risk due to interaction [RERI]) and multiplicative scales. RESULTS: Compared to White participants, non-White participants had 16% higher GM arsenic concentrations and 15-20% higher GM lead concentrations lead. Foreign-born participants had 23% higher GM arsenic concentrations and 29-37% higher GM lead concentrations compared to Canadian-born participants. Prevalence of GDM was greater for non-White compared to White participants (14% vs. 7.2%) and for foreign-born compared to Canadian-born participants (11% vs. 7.9%). Foreign-born participants experienced heightened susceptibility to the effects of lead on risk of PTB (RERI: 0.67, 95%CI: 0.01-1.27). In contrast, PFHxS concentrations were lower in non-White (33%) and foreign-born participants (34%) relative to their counterparts. Prevalence of HDP was also lower in non-White compared to White participants (6.8% vs. 11%) and in foreign-born compared to Canadian-born participants (5.8% vs. 11%). CONCLUSIONS: We identified absolute and relative disparities in prenatal chemical concentrations and prevalence of pregnancy complications in three case studies from a Canadian pregnancy cohort. Our findings provide impetus for future biomonitoring studies that: (a) are larger and more inclusive of racialized and foreign-born populations, (b) use validated tools to directly measure discrimination and structural inequities, and (c) apply intersectional statistical methods.