This mixed-methods dissertation considers the experiences of women who used substances during pregnancy. Retrospective interviews with 15 women, currently accessing inpatient substance abuse treatment, identify trends in women’s experiences prior to accessing these services. Women report being concerned about the impact of their substance use on the developing baby, seeking information, reducing substance use outside of accessing treatment services, and engaging in healthy behaviors to protect the baby from harm. Trends related to trying to reduce harm to the baby during pregnancy are then further explored through quantitative analyses. Data on harm reduction behaviors prior to accessing treatment were collected from an additional 54 women. A clinical and research tool for visually tracking patterns of maternal substance use over the course of pregnancy was developed. This tool identifies the high prevalence of women who decrease their substance use during pregnancy outside of accessing treatment services. Clinical use of this tool is considered. In addition, a questionnaire, designed to identify engagement in harm reduction and health promoting behaviors, was administered. Data suggests that harm reduction and health promotion behaviors are common and tend to begin early on in pregnancy. Women report beginning to decrease their substance use, on average, beginning at the end of the first trimester. The timing of beginning to reduce substance use is not associated with the timing of entering substance abuse treatment in relation to a given pregnancy. However, maternal mental health and perceived barriers to accessing services do predict when, in relation to pregnancy, women enter treatment. As a whole, this research suggests that continued use of substances during pregnancy is not due to indifference towards the developing baby. Instead, women report being concerned about their babies and being engaged in the process of positive self-change. There are public health and clinical implications to these findings. This research suggests the opportunity to build upon the motivation that women have to decrease their substance use. In addition, this research suggests the importance of focusing policy and intervention efforts on addressing perceived barriers to accessing treatment services.