Postpartum Psychosis Readmission and Trauma-Related Mental Health Outcomes in South African Mothers: A Target-Trial Emulation of Community Perinatal Care Contact Windows

Postpartum psychosis is a psychiatric emergency whose readmission risk is shaped by the timing and continuity of community perinatal care contacts, yet the causal estimand for contact-window effects remains poorly specified in low-resource South African settings. The framework specifies the causal estimand, the eligibility criteria, the treatment strategies defined by contact-window timing, the assignment procedure, the censoring and competing-risk structure, and the analytic model required for valid emulation. A design-based power analysis characterised the operating characteristics of the before-after-control-impact estimator under a declared variance structure with between-cluster SD of 6.0, residual SD of 4.5, and intraclass correlation of 0.64. Power was estimated across 2000 replications per design cell for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. The design required 52 clusters to detect a 5 percentage point effect at 80% power. The framework clarifies how contact-window strategies can be compared without the immortal-time and confounding biases that afflict naive observational comparisons, and it identifies the design conditions under which target-trial emulation can support causal inference about perinatal care continuity in South African maternal mental health services.