What factors influence contraceptive counselling readiness among Vietnamese medical students? A nationwide study protocol applying the extended theory of planned behaviour (the V-COC study).

introductionContraceptive counselling is a key preventive intervention for reducing unintended pregnancies and unsafe abortions. In a setting such as Vietnam, where contraceptive use is prevalent, the quality and consistency of counselling provided by future physicians are critical. Although this is a core competency in medical education, evidence suggests that medical students demonstrate deficits in applied knowledge, skills and confidence regarding counselling. Evidence regarding medical students' intentions to provide contraceptive counselling in Vietnam remains limited and has not been systematically examined. METHODS AND ANALYSIS: A nationwide cross-sectional study will be conducted from October 2025 to October 2026 at 12 medical universities representing three distinct regions. Self-administered online questionnaires (via KoboToolbox) will be distributed to first-year to sixth-year medical students. This protocol describes a two-phase study. Phase 1 (scale development and validation; n=600, including pilot and psychometric evaluation) aims to develop and validate the Extended Theory of Planned Behaviour (E-TPB) scales (Knowledge, Attitude, Subjective Norms, Perceived Behavioural Control, Intention). This phase uses the Content Validity Index, Classical Test Theory and Item Response Theory Two-Parameter Logistic to generate latent trait scores for Knowledge, followed by exploratory factor analysis, confirmatory factor analysis (CFA) and assessment of convergent and discriminant validity. Phase 2 (main survey; n=1300) describes the current status by academic year, gender and institution. Simultaneously, the E-TPB model will be tested using Covariance-Based Structural Equation Modelling to estimate standardised path coefficients and mediation effects (5000 bootstrap samples). A multigroup SEM will be conducted to test measurement/structural invariance and to compare key groups (gender; preclinical vs clinical). Missing-data handling will prioritise full information maximum likelihood for CFA/SEM, with strict adherence to predefined quality control criteria. ETHICS AND DISSEMINATION: The study protocol was formally approved by the Institutional Ethical Review Board for Biomedical Research at Hanoi Medical University on 3 March 2026 (Approval No. 120/GCN-KHCN). Results will be published in international peer-reviewed journals and sent to participating medical universities.