Prenatal exposure to ultrafine particles and positive screening for postpartum depression: a prospective pregnancy cohort in Shanghai, China.

Postpartum depression is a major maternal and child health concern, but evidence regarding prenatal exposure to ultrafine particles (UFPs) remains limited. This prospective two-center pregnancy cohort in Shanghai included 2,647 pregnant women. Residential prenatal exposures to UFPs and PM2.5 were estimated for the first, second, and third trimesters and the full pregnancy. Depressive symptoms were assessed at 6-10 weeks postpartum using the Edinburgh Postnatal Depression Scale, with a score ≥10 defined as positive screening for postpartum depression. Associations were evaluated using multivariable logistic regression, two-pollutant models, joint-trimester logistic regression, exploratory stacked logistic generalized estimating equations, restricted cubic splines, and interaction analyses. The prevalence of positive screening for postpartum depression was 20.4%. After adjustment for potential confounders, an IQR increase in first-trimester UFPs exposure was associated with higher odds of screen-positive postpartum depression (OR = 1.252, 95% CI: 1.065-1.471), as was an IQR increase in full-pregnancy UFPs exposure (OR = 1.104, 95% CI: 1.047-1.164). These associations persisted after adjustment for PM2.5, whereas PM2.5 showed no stable independent association. Sensitive-window analysis supported the first trimester as the main window of association, and infant-sex interaction analysis suggested a stronger association among pregnancies with male infants. These findings suggest that prenatal UFPs exposure, particularly during early pregnancy, may be associated with higher odds of positive screening for postpartum depression, highlighting the potential relevance of ultrafine particle number concentration in perinatal environmental health research.