Oral health during pregnancy is a critical factor in preventing caries in both mothers and children. Croatia currently lacks validated psychometric instruments for reliably as-sessing knowledge, attitudes, and oral hygiene practices in the general population. This study aimed to develop and validate a comprehensive instrument for this purpose in Cro-atia and internationally. Following Consensus-based Standards for the selection of health Measurement Instruments (COSMIN) guidelines, an initial item pool was generated through literature review and expert consultation. The study was conducted from May 2024 to February 2025 in primary healthcare settings across Primorje-Gorski Kotar County (PGC). The validation study included 319 pregnant women. Exploratory factor analysis (EFA) revealed a six-factor structure with acceptable to strong factor loadings (ranging from 0.423 to 0.984). The instrument showed acceptable to good internal consistency (Cronbach’s α = 0.61–0.87) and excellent test–retest reliability (Pearson r = 0.993). Results indicated that knowledge about oral health was independent of attitudes and practices during pregnancy, while regression analysis suggested that pregnant women's behaviors are influenced by complex factors beyond those captured in the initial study model. This newly developed and validated questionnaire is a reliable public health tool for systematic data collection, supporting targeted educational interventions to prevent caries and pro-mote oral health among pregnant women.