Prenatal exposure to particulate matter and postpartum depression: the interplay with prenatal stress

Postpartum depression (PPD) is a global health issue associated with high levels of maternal morbidity. We previously found that higher exposure to particulate matter (PM 2.5 ) during pregnancy is associated with PPD. However, the modifying role of prenatal stress on this relationship is unclear. We measured prenatal stress in the PROGRESS cohort ( n = 585 mothers) using negative life events (NLE) and perceived stress score (PSS). Daily residence level of PM 2.5 estimates generated from a spatiotemporal model were averaged over pregnancy. PPD was assessed using the Edinburgh Postnatal Depression Scale (EPDS ≥ 13) and categorized as prevalent PPD (EPDS ≥ 13 at 6 months). Modified Poisson regression was used to evaluate the association between PM 2.5 and PPD, stratified by NLE and PSS scores, dichotomized at the median (low/high). We repeated the analyses with chronic depression, new-onset PPD, including using trimester-specific PM 2.5 exposure, and with another proposed cut-off for Mexico (EPDS ≥ 10). Each 5-µg/m³ increase in average pregnancy PM 2.5 exposure was associated with 130% higher risk of prevalent PPD (EPDS ≥ 13) among mothers with a lower PSS (RR: 2.30, 95% CI: 1.28–4.16) compared to those with a higher PSS. The risk of new-onset PPD (EPDS ≥ 13) at 6 months per 5-µg/m³ increase in PM 2.5 during pregnancy was over two-fold higher among mothers with a lower PSS (RR: 2.27, 95% CI: 1.17–4.41) compared to those with a higher PSS, and with a higher NLE (RR: 2.84, 95% CI: 1.38–5.85) score compared to those with a lower NLE score. The effect of PM 2.5 on PPD was particularly evident for PM 2.5 exposure during the second trimester of pregnancy. Similar findings were observed for an EPDS ≥ 10. The risk of PPD from PM 2.5 exposure was enhanced in mothers with lower PSS or higher NLE scores, especially during the second trimester of pregnancy, 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.