Mandatory Provider-Initiated HIV Testing in Kenyan Public Antenatal Systems: Target-Trial Emulation of Uptake and Postpartum Care Disengagement

Kenya's public antenatal system mandates provider-initiated HIV testing, yet the causal effect of this policy on postpartum care disengagement remains poorly identified because women who accept testing differ systematically from those who do not. The analysis characterises the operating characteristics of the design across 2000 replications per cell for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. Power to detect a 5-percentage-point effect at 80% power required 52 clusters, exceeding the largest design cell. Minimum detectable effects at 80% power declined with cluster count, and the receiver operating characteristic confirmed acceptable discrimination. The framework clarifies that mandatory testing's estimated effect on postpartum disengagement is bounded by design constraints that current Kenyan implementation cannot satisfy, and that target-trial emulation offers a defensible inferential route only when cluster counts exceed those typically available in county-level rollouts.