Substance use during pregnancy has no safe thresholds, is highly associated with abortion and maternal and child mortality, in addition to other short, medium, and long-term negative outcomes. Thus, this dissertation aims to contribute to the understanding of substance use during pregnancy. ARTICLE 1 is a translation and adaptation of a measure for the assessment of risk perception of substance use. In general, the measure made it possible to associate earlier ages of substance use with a lower perception of risk, as well as to differentiate regular users of substances from non-users, with the former presenting a lower perception of risk in general. Comparing non-nulliparous women with and without a history of substance use during pregnancy, we observed that the perception of risk of substance use in general was the main predictor of substance use during pregnancy, in addition to knowledge about the dangers for development. The results suggest that perhaps more important than preventive work with pregnant women alone, investing in promoting substance awareness at an early stage is a more effective strategy to prevent substance use during pregnancy.