Placental toxic metal concentrations and preterm birth: Modification by social stressors

The placenta facilitates vital nutrient and gas exchange between mother and fetus. Metals such as cadmium (Cd), lead (Pb) and arsenic (As) have been associated with decreased placental vascularization, suboptimal invasion, and poorer birth outcomes. Although exposure to these chemical stressors often co-occurs with social stressors, few studies have evaluated the effects of these chemical stressors in the context of social stressors. Herein, we evaluate relationships between chemical stressors and birthweight, gestational age at delivery, and placental weight in the context of social stress. We used Inductively coupled plasma mass spectrometry (ICP-MS) to measure a suite of metals including Cd, Pb and As in fetal placentae of three groups: 62 non-Hispanic white (NHW), 164 non-Hispanic black (NHB), and 84 Hispanic participants. We used Kruskal-Wallis tests to assess overall differences in toxic metal concentrations by for each group, followed by pairwise Wilcoxon rank-sum tests for comparisons between specific groups. Multivariable linear regression models were used to evaluate whether the associations between toxic metals and birth outcomes varied in the offspring of women with or without adverse childhood experiences (ACEs), financial stress, and perceived discrimination. Placental Cd levels for NHB were significantly higher than in Hispanic and NHW participants (p < 0.05), a difference not explained by established exposures such as maternal smoking or obesity. Further analyses revealed that in NHB, significant effects of Cd on shorter gestational age at delivery, birthweight and lower placental weight were apparent only in offspring of parents reporting the existence of ACEs. (p < 0.05). While sample size limits inference, these data support the hypothesis that social stressors interact with environmental contaminants to influence poor birth outcomes. Larger studies are needed to clarify these findings.