Background <p>Sleep quality during pregnancy and the postpartum period is increasingly acknowledged as a critical influencing factor of postpartum. However, the complexities of this relationship, particularly the core depressive symptoms across varying sleep quality trajectories, remain poorly understood.</p> Methods <p>This study included 372 participants from the “Be Resilient to Postpartum Depression” cohort, with data collected at four intervals spanning early pregnancy to 42 days after childbirth. Validated instruments were used to evaluate both sleep quality and postpartum depression. Data analysis employed group-based trajectory modeling and computer-simulated network analysis.</p> Results <p>Two distinct trajectories of sleep quality were identified: “increasingly poor” trajectory (41.4%), which exhibited a markedly higher rate of postpartum depression (<i>OR</i> = 2.75, <i>P</i> &lt; 0.001), and “stably good” trajectory (58.6%). Within the “increasingly poor” trajectory, the symptom “Things have been getting on top of me” emerged as both the core and aggravating symptom. In the “stably good” group, the core and aggravating symptom was “I have felt scared or panicky for no very good reason.” Additionally, “I have been anxious or worried for no good reason” and “I have been so unhappy that I have had difficulty sleeping” were identified as key symptoms associated with alleviating depressive symptoms in the “increasingly poor” and the “stably good” groups, respectively.</p> Conclusions <p>The study underscores the heterogeneous nature of sleep quality trajectories and their distinct associations with postpartum depressive symptoms, highlighting the necessity for tailored mental health interventions.</p>