Maternal Trauma Disclosure and Perinatal Mental Health Service Engagement in South African Midwife Obstetric Units: A Target-Trial Emulation of Routine Enquiry Implementation

Routine enquiry for maternal trauma in South African midwife obstetric units is widely recommended but inconsistently implemented, and the causal effect of disclosure on subsequent perinatal mental health service engagement remains poorly identified because disclosure is neither randomised nor ignorable. No observational data are used or claimed. Under a declared variance structure with between-cluster standard deviation 6.0, residual standard deviation 4.5 and intraclass correlation 0.64, power was estimated across 2000 design cells for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points.54 clusters are required to detect a 5 percentage point effect at 80% power, that the minimum detectable effect falls steeply as clusters increase from 8 to 24 and then flattens, and that the estimator's confidence intervals widen disproportionately at small cluster counts. The contribution is a design specification that separates the causal question from the implementation question, allowing future evaluations of routine enquiry to be powered and interpreted against explicit assumptions rather than post hoc rationalisation.