Introduction: Oral health disorders in a pregnant woman have an adverse impact on the child’s health. A high maternal level of cariogenic bacteria can significantly increase the risk of tooth decay in the child. There is a positive correlation between increased plaque accumulation and premature birth and also low birth weight. Aim and methods: The aim of this study was to discuss the level of knowledge on the aetiology and prevention of tooth decay among pregnant women based on an original survey conducted in 2022 and to compare the results with a survey conducted in 2015 under the affiliation of the Warsaw Medical University, entitled “Awareness of pregnant women about preventing early childhood caries”. Both studies were subjected to a statistical analysis using Spearman’s rank correlation (p < 0.05). Additionally, PubMed data and current literature were used in writing this paper. Literature review: The analysis in both cases revealed a positive correlation between the level of knowledge and the education level of the respondents. In the 2015 group, 10% of expectant mothers knew when their first dental visit should occur, while this percentage rose to 51.9% in the 2022 group. The increase in the level of knowledge is also evident when considering questions about oral care before tooth eruption. Summary: The level of knowledge on the aetiology and prevention of tooth decay among pregnant women has increased compared to previous years and can be considered high. Further education is still needed.