Air pollution and postpartum depression: the interplay with prenatal stress

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.