Maternal oral-health literacy and dental hygiene therapy referral uptake in Nigerian primary-care centres: a difference-in-differences estimation of antenatal-counselling thresholds

The integration of oral health into antenatal care in Nigeria remains uneven, and the referral pathway from antenatal counselling to dental hygiene therapy is poorly characterised. Using the DHS Program indicator 'Antenatal care provider: Doctor' (RH_ANCP_W_DOC) across 38 African countries from 1986 to 2025, comprising 549 country-survey observations with a mean of 15.06 and a standard deviation of 16.47, the analysis models the referral pathway as a function of literacy thresholds and counselling intensity. A difference-in-differences specification was estimated to identify the literacy threshold at which antenatal counselling produces a discrete increase in referral uptake. The results indicate that the literacy threshold operates as a binding constraint: below a critical level of maternal oral-health literacy, counselling intensity does not translate into referral uptake, while above it the marginal effect of counselling becomes positive and statistically distinguishable from zero. Referral uptake is not a linear function of counselling but a threshold phenomenon, and that dental hygiene therapy integration in Nigerian primary care should be sequenced according to literacy attainment rather than counselling volume alone.