Purpose <p>Prenatal stress affects up to 74% of expectant mothers and has been implicated in shaping early child development. This study aims to examine the associations between both subjective (self-reported) and objective prenatal stress and infant temperament at 12 months of age. Additionally, we investigate whether maternal postpartum depression (PPD) mediates these associations.</p> Methods <p>We analyzed data from 1,510 mother-infant dyads in the French EDEN birth cohort. Prenatal stress was assessed using the State Anxiety Inventory (STAI), the Center for Epidemiological Studies Depression Scale (CES-D), and a measure of negative life events (NLEs). Infant temperament at 12 months was measured using the Emotionality Activity Sociability (EAS) questionnaire. Adjusted logistic regression models and mediation analyses were used to assess direct and indirect effects.</p> Results <p>Prenatal anxiety was associated with greater infant sociability, while prenatal depression predicted increased emotionality and shyness. Objective stress was related to lower infant activity. Mediation analyses revealed that PPD partially mediated the effects of prenatal depression and anxiety on infant emotionality and shyness, accounting for approximately 32% of the association between prenatal depression and infant emotional temperament. No mediation effect was found for the activity domain, although a small inverse direct association was observed.</p> Conclusion <p>Our findings suggest that maternal prenatal stress influences infant temperament in a trait-specific manner and that PPD plays a mediating role in certain domains. These results highlight the importance of addressing both prenatal and postnatal maternal stress when considering early emotional and behavioral development in children. Clinical trial number: not applicable.</p>