Purpose: To investigate if pregnancy represents a period of increased risk of non-cavitated dental caries related to changes in saliva and oral health behaviours. Materials and Methods: A non-randomised longitudinal study was performed with 27 pregnant women and 25 non-pregnant women, who were evaluated twice with the same time gap (24 weeks on average). At the first visit sociodemographic and oral health-related behaviours were assessed through a structured questionnaire. At the second visit changes related to eating sweet snacks and oral hygiene habits were also assessed. In both visits the surface-related caries status was evaluated according to ICDAS II criteria. Calculation of D0 (Sound), D1–2 (visual changes) and D3–4 (precavitated caries lesions) Index was based on data collected from clinical examination. Saliva pH and saliva flow rate were also assessed. Results: Throughout pregnancy, a statistically significant increase of eating sweet snacks between main meals was reported, with no effective adaptation of oral hygiene habits. In comparison to the non-pregnant group, pregnant women presented a lower saliva pH at both the first and second visit, p 0.0005. During the follow-up period, a decrease in the frequency of caries-free surfaces was observed in the pregnant women (p = 0.004) and an increase in precavitated caries lesions (p = 0.011). Conclusion: The main results support the hypothesis that during pregnancy women are prone to enamel demineralisation, namely, to exhibiting additional lesions characterised by precavitated caries lesions. Keywords: pregnancy, dental caries, saliva pH, oral hygiene, diet