Background <p>Postpartum birth trauma symptoms, encompassing psychological and physical sequelae related to childbirth experiences, pose a significant threat to maternal well-being. These symptoms, as measured in this study, are not equivalent to a clinical diagnosis of post-traumatic stress disorder (PTSD) but reflect self-reported experiences based on the City Birth Trauma Scale.</p> Methods <p>This multi-center cross-sectional survey enrolled 230 women at 42 days postpartum from four hospitals in Shanghai between February and July 2024. Birth trauma symptoms were assessed using the Chinese City Birth Trauma Scale. Emotional and informational support expectation gaps were calculated as the difference between the importance score and the actual support score in each domain of the Postpartum Social Support Scale (gap = importance − actual), with larger positive values indicating greater unmet needs. Partner involvement was classified as high, medium, or low. Multiple linear regression identified independent predictors of trauma severity.</p> Results <p>Birth trauma symptoms were assessed using the Chinese City Birth Trauma Scale. The full sample was analyzed for symptom severity, while the proportion of participants scoring above the ≥ 28 cut-off (Brazilian validation study) was used to estimate the prevalence of clinically significant symptoms. Of all participants, 54.3% scored ≥ 28, indicating clinically significant childbirth-related PTSD symptom levels on the City Birth Trauma Scale, with a mean trauma score of 45.12 ± 16.25. Larger emotional (<i>β</i> = 0.102, <i>p</i> = 0.018) and informational (<i>β</i> = 0.158, <i>p</i> = 0.024) support gaps were independently associated with greater trauma severity, as were low education (<i>β</i> = 0.281, <i>p</i> &lt; 0.001), low household income (<i>β</i> = 0.172, <i>p</i> = 0.014), formula feeding (<i>β</i> = 0.180, <i>p</i> = 0.010), and low partner involvement (<i>β</i> = 0.165, <i>p</i> = 0.018). High partner involvement demonstrated a protective effect comparable to socioeconomic factors. The final model explained 29% of the variance in trauma scores.</p> Conclusions <p>Inadequate partner involvement and larger emotional and informational support gaps are significantly associated with greater postpartum birth trauma severity. Interventions should prioritize partner-inclusive care and targeted support to address unmet informational and emotional needs. Routine psychosocial screening at postpartum follow-up may facilitate early identification and intervention for at-risk women.</p>