Objectives: This study aims to find out whether offering prenatal screening for Down syndrome and neural tube defects influences pregnant women’s attitudes toward having a screening test. Methods: Women were randomised into a group that was offered prenatal screening and a group that was not offered screening (controls). Both groups completed questionnaires before screening was offered, after the offer (not the control group), and in the last trimester of pregnancy. Results: Women with a neutral attitude at baseline who accepted the screening test had a more positive attitude, decliners became more negative and the attitude of the control group did not change. Conclusion: Offering prenatal screening triggers a change in some pregnant women’s attitude regarding prenatal testing. This instability of women’s attitudes may pose a problem for determining whether some women made an informed choice.