Dental hygiene therapy–led maternal oral-health referral and low birthweight in Tanzanian antenatal clinics: a target-trial emulation of referral-timing heterogeneity

Dental hygiene therapy–led maternal oral-health referral is a plausible lever against low birthweight in Tanzanian antenatal clinics, but the timing of referral within gestation is heterogeneous and the design characteristics needed to detect a clinically meaningful effect are unclear. the present analysis treats the referral-timing question as a target-trial emulation problem and characterises the operating characteristics of a before-after-control-impact (BACI) estimator under a declared variance structure. No observational data are used or claimed. The analysis assumed a between-cluster standard deviation of 6.0, a residual standard deviation of 4.5 and an intraclass correlation of 0.64, and evaluated power 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. Under these assumptions, 52 clusters were required to detect a 5 percentage-point effect at 80% power. The intraclass correlation of 0.64 dominated the design: at 8 and 16 clusters, power remained low even for an 8 percentage-point effect, and only at 32 clusters did the power curves approach conventional thresholds for the larger effects. The minimum detectable effect at 80% power fell steeply as cluster count rose from 8 to 32. The results imply that referral-timing heterogeneity cannot be resolved by antenatal-clinic BACI designs of the size typically available in Tanzanian districts, and that dental hygiene therapy–led referral trials should be powered for cluster-level variation rather than for individual-level birthweight contrasts.