Racial/ethnic disparities in phthalate metabolite mixtures and risk of preterm birth: A pooled study of 16 US cohorts

Abstract

BACKGROUND AND AIM. Environmental phthalate exposure is ubiquitous in pregnancy and may be a risk factor for preterm delivery. In the United States (US), large racial/ethnic disparities in phthalate exposure may be an important contributor to the racial/ethnic disparities in preterm birth. Utilizing the largest study of phthalates and preterm birth to date, we 1) investigated racial/ethnic disparities in phthalate exposure and 2) estimated how racial/ethnic disparities in preterm birth might improve by equitably reducing phthalate exposure. METHODS. We pooled individual-level data from 16 US cohorts (N=6,045) on 9 prenatal urinary phthalate metabolites. We categorized participant race/ethnicity as non-Hispanic white (43%), non-Hispanic Black (13%), Hispanic/Latina (38%), or Other (5%; based on sparsity of sub-categories). We investigated confounder-adjusted differences in urinary phthalate metabolite concentrations by maternal race/ethnicity. We used g-computation to estimate changes in preterm birth by race/ethnicity after simultaneous, racial/ethnic-specific reductions in the concentration of all 9 phthalate metabolites. Our hypothetical intervention eliminated racial/ethnic disparities in the distributions of metabolite concentrations. RESULTS. For 8 of the 9 phthalate metabolites, concentrations were highest among non-Hispanic Black participants and lowest among non-Hispanic whites. Covariate-adjusted differences in metabolite concentrations were most pronounced for monoethyl phthalate and mono-isobutyl phthalate, which were 143% (95% confidence interval [95CI]: 114%, 175%) and 80% (95CI: 66%, 95%) higher among non-Hispanic Black compared to non-Hispanic white participants, respectively. The hypothetical intervention to simultaneously reduce concentrations of metabolites by race/ethnicity, principally among non-white racial/ethnic groups, showed significant reductions in preterm birth. For non-Hispanic Black participants, the pre- and post-intervention probability of preterm birth was 117 (95CI: 94, 141) and 88 (95CI: 61, 118) preterm per 1,000 live births, respectively, representing a relative reduction of 25% (95CI: 16%, 35%). CONCLUSIONS. Considerable differences in exposure to phthalates could play an important role in the racial/ethnic disparities in preterm birth within the US.