Air pollution and postpartum depression: the interplay with prenatal stress

Abstract Background Postpartum depression (PPD) is a global health issue that can lead to high levels of maternal morbidity. We previously found that ambient air pollution (PM 2.5 ) during pregnancy is associated with PPD. However, the modifying role of psychosocial stress on this relationship is unclear. Methods We measured pregnancy stress in the PROGRESS cohort (n = 475 mothers) using negative life events (NLE) and perceived stress score (PSS). We assessed the modifying role of NLE and PSS on the association between prenatal PM 2.5 exposure and PPD at 6 months. Daily residence level PM 2.5 estimates generated from a spatiotemporal model was averaged over pregnancy. PPD was assessed using the Edinburgh Postnatal Depression Scale (EPDS ≥ 13) and categorized as chronic depression (EPDS ≥ 13 during pregnancy and at 6 months), new-onset PPD (EPDS < 13 during pregnancy and EPDS ≥ 13 at 6 months), or prevalent PPD (EPDS ≥ 13 at 6 months, regardless of EPDS score during pregnancy). Modified Poisson regression evaluated the association between PM 2.5 and PPD, stratified by NLE and PSS scores, dichotomized around the median (low/high). We repeated the analyses with other proposed EPDS cut-offs for Mexico (EPDS ≥ 10 and ≥ 12). Results Each 5-µg/m³ increase in average pregnancy PM 2.5 exposure was associated with 129% higher risk of prevalent PPD among mothers with low PSS (RR: 2.29, 95% CI: 1.17–4.47). The risk of new-onset PPD at 6 months per 5-µg/m³ increase in PM 2.5 during pregnancy quadrupled among mothers with low PSS (RR: 4.58, 95% CI: 1.83–11.49) and high NLE (RR: 4.71, 95% CI: 1.72–12.92) scores. Similar findings were observed with an EPDS ≥ 10 or EPDS ≥ 12 cut-off. Conclusion The risk of PPD from PM 2.5 exposure was enhanced in mothers with low PSS or high NLE scores, especially new-onset PPD, regardless of the EPDS threshold used. These findings suggest that well-characterized stress phenotyping during pregnancy may help identify which women are at-risk for depression.