# Air pollution and postpartum depression: the interplay with prenatal stress

## TL;DR

This study shows that air pollution during pregnancy increases the risk of postpartum depression, especially in mothers with low stress or high negative life events.

## Contribution

The study reveals how psychosocial stress modifies the link between air pollution and postpartum depression.

## Key findings

- Higher PM2.5 exposure during pregnancy was linked to a 129% increased risk of prevalent PPD in mothers with low perceived stress.
- New-onset PPD risk quadrupled with PM2.5 exposure among mothers with low perceived stress or high negative life events.
- Findings were consistent across different EPDS thresholds for depression diagnosis.

## Abstract

Postpartum depression (PPD) is a global health issue that can lead to high levels of maternal morbidity. We previously found that ambient air pollution (PM2.5) during pregnancy is associated with PPD. However, the modifying role of psychosocial stress on this relationship is unclear.

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 PM2.5 exposure and PPD at 6 months. Daily residence level PM2.5 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 PM2.5 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).

Each 5-μg/m3 increase in average pregnancy PM2.5 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 PM2.5 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.

The risk of PPD from PM2.5 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.