Dental hygiene therapy–led community periodontal therapy and adverse pregnancy outcomes in Rwandan health centres: a target-trial emulation of antenatal referral timing

Periodontal disease in pregnancy is associated with adverse birth outcomes, but whether dental hygiene therapy–led community periodontal care reduces that risk, and when antenatal referral should occur, remains unresolved. The design characterises the operating characteristics of the before-after-control-impact estimator 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. The analysis indicates that 54 clusters are required to detect a 5 percentage point effect at 80% power. Referral timing, rather than therapy intensity alone, is the parameter that determines whether community periodontal care can plausibly affect birth outcomes, and it specifies the design conditions under which that proposition can be tested without confounding by gestational age at enrolment.