Background Being obese or gaining excessive weight during pregnancy can increase health risks for mother and baby. Adopting a healthy diet and increasing physical activity reduces these risks and has long-term health benefits for women. Despite this, women do not always maintain a healthy lifestyle during pregnancy. Aim To explore the factors that encouraged and prevented a diverse group of women to maintain a healthy lifestyle during pregnancy. Methods A total of 12 women participated in semi-structured qualitative interviews, underpinned by the theory of planned behaviour. Interviews were audio recorded, transcribed verbatim then subject to deductive thematic analysis. Findings Four themes emerged: women's knowledge of a healthy lifestyle, sociocultural influences, physical health and health professional support. These influenced women's intentions and actual behaviours during pregnancy. Conclusions Enhanced health professional advice may motivate women to adopt a healthy lifestyle during pregnancy. This could be through new means such as health technology.