Background and Objective: Prenatal diagnosis for chromosomal anomalies is frequently used worldwide. It is important that pregnant women receive adequate counselling to make informed decisions regarding prenatal diagnosis. The aim of this study was to explore what factors influence pregnant women's decision-making process when accepting or declining prenatal screening and diagnosis. Methods: A qualitative study using inductive qualitative content analysis. Individual, semi-structured phone interviews were carried out during a five-month period in 2016-2017 with 24 pregnant women in the first trimester, living in a medium-sized Swedish city. Findings: Two main themes emerged: (1)"Individual factors - The women's experiences, perceptions and values" with three categories "Attitude towards anomalies", "Worry and need for reassurance", "Self-perceived risk" and (2)"External factors - The women's perception of the test and others' views" with two categories "Test characteristics" and "Influence from others". Conclusions: Pregnant women's decision-making process regarding prenatal tests is multidimensional, affected by both individual factors such as experiences, perceptions and values, and external factors such as test characteristics and influence from others. Information about both test characteristics and the conditions tested is of help pregnant women in the decision-making process since it provides a better understanding of how having a child with the condition in question can affect them and their family. It is important that healthcare professionals giving information about and offering prenatal tests for chromosomal anomalies are aware of how their attitudes can influence women's decisions.