Background: Evidence suggests that cigarette smoking and alcohol consumption during pregnancy negatively impacts fetal health. Health agencies across countries have developed specific guidelines for health professionals in perinatal care to strengthen their role in smoking and alcohol use prevention. One such example is the “Guideline on Screening and Counselling for prevention of cigarette smoking and alcohol consumption before, during, and after pregnancy” introduced by the Swiss Midwives Association in 2011. The current study assesses the changes in midwives’ engagement in smoking and alcohol use prevention before (2008) and after the introduction of the Guideline (2018). Further, the current study examines differences across regions (German vs. French speaking regions), graduation years (before and after the introduction of the Guideline) and different work settings (hospital vs. self-employed). Methods: Survey data were collected in 2008 (n = 366) and in 2018 (n = 459). Differences in how midwives engaged in smoking and alcohol use prevention between 2008 and 2018 were assessed with chi-square tests, as were differences across German and French speaking regions, graduation years (before and after the introduction of the Guideline) and across different work settings (working in hospitals or as self-employed). Results: An increase in midwives’ awareness of the risks of consuming even small quantities of cigarettes and alcohol for the unborn child between 2008 and 2018 is evident. Explaining the risks to pregnant women who smoke or use alcohol remained the most frequently reported prevention strategy. However, engagement with more extensive smoking and alcohol use preventive strategies across the whole course of pregnancy, such as assisting women in the elaboration of a plan to stop smoking/alcohol use, remained limited. Conclusions: Seven years after its introduction, the effectiveness of the Guideline in increasing midwives’ engagement in smoking and alcohol use prevention appears limited despite midwives’ increased awareness.