The population–environment–food nexus is a sustainability challenge for the Global South, and for Africa in particular, where rapid human population growth typically overlaps with high levels of food insecurity and environmental degradation. In this context, it is important to understand the reasons driving high fertility in these regions. Here, we examined possible determinants of women’s fertility preferences in rural southwestern Ethiopia. Using a survey tool (n = 120), we assessed women’s perceptions of four key environmental stressors, namely food insecurity, environmental degradation, human population growth, and land scarcity. Through statistical modelling we tested whether there was a relationship between perceptions of future trends in these stressors and women’s fertility preferences; expressed as their desired number of children and use of family planning methods. This analysis was complemented by a qualitative content analysis of the survey’s open-ended questions, to contextualize and interpret the quantitative data. Our quantitative results indicated that perceptions of future trends in key stressors had little effect on fertility preferences of respondents, with the exception of perceptions of human population growth. Our qualitative data suggested that this may be due to the influence of social-cultural norms and religion, decision-making with the husband, as well as a perceived utilitarian value of children. These findings have important implications for the development of interventions to slow down human population growth. Our findings suggest the need to look beyond improved physical access to family planning, and develop a new suite of deliberative approaches that engage with social norms, religion, and gender equity.