OBJECTIVE The study aims to analyse the reasons underpinning women's refusal to undertake Down's syndrome screening (DSS) by maternal serum testing (MST). METHODS A retrospective, mixed methods sequential approach was used. An online survey on women's experience of prenatal testing followed by in-depth interviews were conducted, with women over 18 years old, who had been pregnant within five years prior to the study. Altogether, 1726 responses were gathered, of which 217 related to women who had refused MST. The study compares the women who refused MST with women who accepted it on sociodemographic characteristics, the evolution and experience of the pregnancy, their knowledge about Down's syndrome (DS). It also utilises survey comments and five in-depth interviews to explore, using Thematic Analysis, the reasons for refusing MST. RESULTS To refuse MST is cognitively demanding. Indeed, women who refused MST were better educated, knew more about prenatal diagnosis sequences and DS than women who accepted it. This position is also emotionally challenging as women's interactions with practitioners can put them in difficult situations, where they have to defend their point of view. Reasons for refusing MST go beyond religious beliefs, negative attitudes towards abortion and/or medicalisation of pregnancy. Rather, women's position appears to be driven by a holistic conception of care-based monitoring, values of inclusivity and a desire to remain in control of their pregnancy. CONCLUSIONS It is essential that women feel accepted and supported in their choice to refuse MST. Consequently, it is important for professionals to remain cognisant of the diversity of factors underpinning women's decision, the pressure this position generates and the challenges that come with it.