Objectives. Prenatal health behaviours have significant implications for maternal and child health. Understanding factors that influence prenatal health behaviours is essential to support women’s prenatal psychological and physical health. Examining strategies women report using during this time also provides insight into acceptable and feasible approaches for support. The aim of this study is to examine the role of prenatal maternal stress (PNMS), social support, and knowledge on health behaviours; and to examine women’s engagement in prenatal stress-reduction support.Methods. A cross-sectional study including 252 pregnant women recruited from an antenatal outpatient department in Ireland, and online. Women completed self-reported measures of sociodemographics, PNMS, social support, knowledge, health-behaviours, and stress-reduction strategies. Correlational analyses and hierarchical multiple regression analyses were conducted to examine associations between PNMS, social support, knowledge, and health behaviours.Results. PNMS predicted unhealthy eating (β= 0.229). Social support predicted physical activity (β= 0.206), sleep (β= 0.186), and taking vitamins (β= 0.200). Age (β= 0.232) and social support (β= 0.228) predicted healthy eating. Women reported good knowledge of PNMS, health behaviours, discomforts of pregnancy, and parenting. Forty-nine stress-reduction strategies were reported; exercise and connecting with others were the most commonly reported strategies.Conclusions. Social support is an important independent predictor of health behaviours. Lack of associations between PNMS and any health-promoting behaviours suggests different mechanisms of effect of positive and negative psychosocial factors. Interventions incorporating both social-support and stress focused strategies may therefore demonstrate greater benefit for prenatal health behaviour change, with significant benefits for women and children.