Although the importance of the dynamic intra-individual relationship between mother-to-infant bonding and postpartum depressive symptoms has been widely recognized, the complex interplay between them is not well understood. Furthermore, the potential role of prenatal depressive symptoms and infant temperament in this relationship remains unclear. This study aims to examine the bidirectional influence of mother-to-infant bonding on postpartum depressive symptoms within individuals and to elucidate whether prenatal depressive symptoms and infant temperament would influence deviations from stable individual states.

Longitudinal data were collected from 433 women in early pregnancy. Of these, 360 participants completed the main questionnaires measuring impaired mother-to-infant bonding and postpartum depressive symptoms at least once during the postpartum period. Data were collected at early and late pregnancy and several postpartum time points: shortly after birth and at one, four, ten, and 18 months postpartum. We also assessed prenatal depressive symptoms and infant temperament. A random-intercept cross-lagged panel model was used.

Within-individual variability in mother-to-infant bonding, especially anger and rejection, significantly predicted subsequent postpartum depressive symptoms. However, the inverse relationship was not significant. Additionally, prenatal depressive symptoms and difficult infant temperament were associated with greater within-individual variability in impaired mother-to-infant bonding and postpartum depressive symptoms.

The present study demonstrated that the within-individual relationship between mother-to-infant bonding and postpartum depressive symptoms is likely non-bidirectional. The significance of the findings is underscored by the potential for interventions aimed at improving mother-to-infant bonding to alleviate postpartum depressive symptoms, suggesting avenues for future research and practice.