Perinatal Oral Hygiene Counselling Timing and Early Childhood Caries Incidence in Nigerian Primary Care: A Target-Trial Emulation of Antenatal Visit Windows

The timing of perinatal oral hygiene counselling within antenatal care is a modifiable determinant of early childhood caries, yet the visit windows through which such counselling is delivered have not been evaluated as a design problem. No observational data were used or claimed. The analysis characterised the operating characteristics of the design under a declared variance structure with between-cluster SD = 6.0, residual SD = 4.5 and intraclass correlation = 0.640. Power was estimated across 2000 design cells defined by cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points, with 2000 replications per cell. The design required 54 clusters to detect a 5-percentage-point effect at 80% power. Estimated power rose with cluster count and effect size, and the minimum detectable effect at 80% power fell as clusters increased. The intraclass correlation of 0.64 dominated the variance budget and made cluster count the binding constraint on precision. The contribution is a design-level specification of the cluster and effect-size combinations under which a target-trial emulation of antenatal counselling timing can be expected to yield interpretable estimates, together with the boundary conditions under which the before-after-control-impact estimator is and is not adequate for this question.