Pre-exposure prophylaxis discontinuation among pregnant and breastfeeding women initiating antenatal care: a target-trial emulation of integrase-inhibitor regimen effects on maternal HIV acquisition

Pregnant and breastfeeding women who discontinue pre-exposure prophylaxis after antenatal initiation differ systematically from those who continue, and integrase-inhibitor-based antiretroviral regimens may alter both the hazard of maternal HIV acquisition and the probability of discontinuation. Conventional observational contrasts conflate these pathways. the present analysis characterises, by design analysis rather than by field data, how a before-after-control-impact (BACI) target-trial emulation performs when the estimand is the effect of integrase-inhibitor regimen exposure on maternal HIV acquisition among women who discontinue pre-exposure prophylaxis. 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 replications per design cell for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. Fifty-two clusters are required to detect a 5-percentage-point effect at 80% power. The analysis specifies the identifying assumptions, the discontinuation-related threats to exchangeability, and the sensitivity analyses that a substantive emulation would require. The contribution is a design-level account of when BACI emulation can separate regimen effects from discontinuation effects in antenatal cohorts, and of the cluster counts at which that separation becomes statistically credible.